Urban street structure and safety
I grew up in small and mid-sized cities of India in the 1950s. My father worked for the government and the family would move every three years or so. Every time we moved, my brother and I would despair about losing friends but then get involved with the logistics of the move and look forward to settling down in a new city. As young boys, it was not so difficult to make friends in a new place as we would cycle to school and explore our neighbourhood, walking or cycling around. Quite soon we would come to know the local grocer, the book and stationery shop owners and a number of street vendors. If memory serves me right, when we did business with them we were treated as adults and haggled about prices and the products we bought. It was great to be independent and able to buy chana-jor-garam, chuski or chaat without parents’ oversight or teachers’ disapproval. I even remember sneaking out of the house into 45oc midday heat to play with friends as soon as our mother retired for an afternoon siesta.
I recall all this not only with nostalgia (common with people my age) but also concern about the motorization of our cities, which has made our streets unsafe for children and the elderly. Living in Delhi, we denied the pleasure of independence to our daughter, who was not allowed to venture out on a bicycle on the road in front of our house. It’s too unsafe, we thought. But, while at work, I write and lecture about the merits of bicycling and walking! This just about sums up the dilemma most of us are confronted with while imagining the future of our urban spaces.
Many of us struggling with the threat of global warming attend unending seminars on sustainable development. Almost all discussions revolve around conserving energy and finding cleaner sources for the same lifestyle of consumption. Even as we are being assured that there is little to worry about as cars are becoming cleaner and will be ‘non-polluting’, eventually, there is also a lurking fear – more technology and less CO2 alone may not make our cities more liveable for our grandchildren. The threat of crime and traffic accidents will not reduce with reductions in CO2 after the sustainable transport conferences. Nor will the need for people to walk and bicycle to work, for shopping and for entertainment.
Some of this is self-evident if we look at how people move around in cities in the low and middle income countries like India. I believe that Indian cities are in an enviable position of having the possibility to evolve into the most sustainable habitats in the world with human scale living environments if we change our mindset and start looking at the positive attributes along with their shortcomings. A soft state and frequent elections have ensured that western inspired master plans could not be implemented in totality. This has made it possible for our cities to have mixed land use and the possibility for the poor to live interspersed with the rich (although ‘illegally’). Our cities have grown somewhat organically due to the pressure of people’s needs despite the short-term vision of bureaucrats and businesspersons. This, incidentally, happens to converge with the prescriptions of most modern urban planners.
The result is that most people tend to live close to their places of work, except the rich and those poor families evicted by whims of city planners and land mafias. Data available indicate that a majority of trips are less than 5-6 km in length even in large cities. A sprawling Delhi is not like Los Angeles in the USA. In Los Angeles everyone goes long distances from everywhere to everywhere, whereas Delhi functions as a conglomeration of a large number of ‘cities’ in a city. Most people work, live and socialize within their ‘city’. This is an ideal situation to work towards a sustainable future by embracing policies that do not force people to travel long distances.
Most Indian cities have grown after 1960 and all have planned for multiple business districts. In the second half of the 20th century, most families in Indian cities did not own a personal vehicle and so all leisure activity revolved within short distances around the home. In the past two decades, however, vehicle ownership has increased substantially in Indian cities. Delhi has by far the highest ownership levels with 15-20% of Delhi’s families owning a car and about 40% a motorcycle at a very low average per capita income level of about Rs 50,000 per year. Such high levels of private vehicle ownership (including motorcycles) did not happen in western cities until incomes were much higher. Car ownership in all other cities of India is less than half that in Delhi. The high ownership of motorcycles, non-availability of funds to build expensive grade separated metro systems, and official plans encouraging multi-nodal business activity in a city has resulted in the absence of dense high population central business districts. Our cities have developed urban forms that encourage ‘sprawl’ in the form of relatively dense cities within cities. The relative absence of metro rail systems that encourage long distance travel, have helped this form of development in most cities in India.
There are two factors at work here. Low and middle income people do not require a large pool of activities to find work. If businesses are mixed with residential areas, and the lower income people allowed to live everywhere, then the less skilled persons are more likely to find work closer to home. For example, a carpenter does not need a specialized workplace to find a job. Only highly skilled people do, and they have to opt for work locations wherever available. It is this latter minority that needs long distance travel and so they force policies to suit them. This group constitutes a sizeable part of the population in large cities and needs motorized transport, at least for work trips.
Availability of affordable motorcycles and changes in car technology have made it easier for the ‘middle class’ to shift to personalized modes of transport in our cities. Most middle class families did not own air conditioned cars with stereo systems in Europe before 1970. The cars were noisy and occupants exposed to traffic fumes as windows had to be kept open. Under such conditions, the train was much more comfortable. This created a situation where the middle class began to exert political pressure to build a metro system. On the other hand, brand new, quiet, stereo equipped, air conditioned cars are now being sold in India at prices lower than US$ 5,000 and used ones for a quarter that price, making it possible for the middle class, first time car owner to travel with comfort levels Europeans had not experienced until the late 20th century. It is unlikely that air conditioned, comfortable, safe and quiet travel in cars with music in hot and tropical climates can be matched by public transport. Owners of such vehicles would brave congestion rather than the climate on access trips and the jostling in public transport. For public transport to be made a viable option, it must be available closer to home, reduce walking distances, and ensure safety on the streets from both accidents and crime.
What modes of travel people use in cities is decided by a balancing of economic compulsions, comfort and safety. Studies of travel behaviour around the world suggest that people do not necessarily minimize time spent on trips. Most seem to have a personal travel time budget preference and utilize it fully except when circumstances don’t permit them to do so. If provided faster modes of travel, they live further away from work! Public transit is used mainly by those who don’t have a vehicle for personal use or when car use is inconvenient (irritating driving conditions, long distance travel), time wasting, impossible (no parking at destination) or unsafe.
Road Accident Fatality Rates per 100,000 Persons for Indian Cities With Population Greater Than One Million Persons
Safety on access trips to bus or metro stations also emerges as an important concern, especially for women and children. Unless the walking trip is safe from accidents, harassment and crime, people avoid using public transport. Even the best public transport system will not entice people, who have a choice, to use it if their perception of safety remains negative. Therefore, safety is a critical precondition for promoting public transport use.
Most urban rail and bus transport authorities (except the BRT in Delhi) have not made adequate provisions for safe walking and bicycling facilities in their areas of operation. At the same time, the fear of crime and road accidents has considerably increased over the years. This despite an increase in presence of armed police, private guards, CCTV cameras, gated communities and ‘modern’ road building projects, and the highlighting of these issues by the media. Why our cities are not becoming safer is then seen as just a matter of policing, morality and ‘values’. Are there any structural and design issues that also influence how people behave? Does city layout and street design itself decide the level of safety as far as traffic accidents are concerned? This article reports the results of a preliminary investigation regarding these issues.
Road accident fatality rates differ widely from city to city in India. Figure 1 shows the statistics for some of the million plus cities for which data are available.1 The pattern shows that at similar population levels cities experience different death rates even if they are in the same state. The safest cities have death rates about 5-7 times lower than the most unsafe cities, and the differences are greater in cities with a smaller population. It is difficult to explain these large differences by levels of enforcement or behaviour of road users. In any case, details regarding location, road conditions, driver and other accident attributes are not available. Hence, we decided to enquire if such variations exist in other cities around the world.
Road traffic fatality data was collected for 56 cities around the world for the period 2000 to 2003 from the following sources: official internet sites of respective cities/nations, journal publications in the same period, and official city traffic and accident reports. An attempt was made to obtain data for cities representing a wide spectrum of per capita incomes – from the lowest to the highest income cities.
Road Accident Fatality Risk in Different Cities Around the World (airport codes are used to designate different cities)
Figure 2 shows road traffic fatalities per million population for a number of cities around the world. These data show a wide variation across income levels and within similar income levels. The risk varies by a factor of about 20 between the best and the worst cities. Some characteristics are summarized below.
* Overall fatality risk in cities with very low per capita incomes (less than USD 1,000) and those with high incomes (greater than USD 10,000) are similar.
* There is a high variability in fatality risk in middle income countries (USD 10,000-20,000).
* There is a great deal of variation even in those cities where the per capita income is greater than USD 20,000 per year.
These patterns indicate that it is not sufficient to merely have the safest vehicle technology to ensure low road traffic fatality rates uniformly across cities in those locations. Even in low and middle income countries, the absence of funds and possibly unsafe roads and vehicles does not mean that all cities have high overall fatality rates. Provision of safely designed roads and modern safe vehicles may be a necessary, but not a sufficient condition for low road fatality rates in cities. The fact that there are wide variations in overall fatality rates among high income cities, where availability of funds, expertise and technologies are similar, indicates that other factors like land use patterns and exposure (distance travelled per day, presence of pedestrians, etc.) also play an equally important role. This is probably why many European cities tend to have lower fatality rates than those in the US.
Vehicle speed is strongly related to both the probability of a crash and the severity of injury – a 1% increase in average speeds can result in a 3 to 4% increase in fatalities.2 This may be a reason why some cities in middle income countries have high fatality rates, because they have higher vehicle ownership than low income countries and road designs encourage unsafe speeds without adequate attention to road safety. Similarly, cities with greater traffic congestion (hence lower speeds) have lower rates than those with less congestion, though their incomes may be similar; Mumbai, with higher congestion, has lower rates than Delhi with lower congestion levels, and New York has a lower rate than Houston, also in the US.
The above discussion indicates that RTI fatality rates do not depend upon road and vehicle design alone, but also on exposure, incomes, traffic management and policing, which in turn depend on societal income levels. To eliminate the impact of income, we decided to examine the experience of cities within the US. We selected the US because researchers there generate a large amount of scientific information on road safety and make available detailed data. We also expect variations in enforcement, technology, funds and ‘culture’ to be lower among US cities than comparing cities across countries.
To obtain RTI fatality data for US cities, we used the Fatality Analysis Reporting System (FARS) (http://www-fars.nhtsa.dot.gov/Main/index.aspx) files to obtain total number of fatalities for all cities for the years 2004-2008. The variables included were: fatalities by road user type, location of fatalities by class of road, number of lanes at location of the crash, and whether the crash occurred at a junction or mid-block. Population data for all cities was obtained from the US Census Bureau data files (www. census.gov). We used the average fatalities per year per unit population of the city to estimate risk of road users.
Average RTI Fatality Rates Per 100,000 Persons (years 2004-2008) for All Cities (172 Cities) for Population > 100,000 Persons
Figure 3 shows data for cities with a population greater than 100,000 persons. The following trends were discernible:
* Cities with the highest fatality rates can have rates that are greater by a factor of 3-6 than those with the lowest rates.
* The differences between highest rates and lowest rates tend to decrease with an increase in city population; however, there is a wide scatter at all population levels.
Figure 3 shows examples of two cities, Jacksonville in Florida and San Francisco, both with populations around ~800,000 but with fatality rates varying by a factor of four. Two much smaller cities, Aurora in Illinois and Ontario in California with populations around ~180,000, show similar differences. It is interesting that two cities in the same country can have very different fatality rates, though their income levels, traffic enforcement patterns and traffic rules may be similar.
Out of this sample we randomly selected 10 cities with the highest accident rates and 10 with the lowest rates, and used the high and low crash cities for comparison. It showed a difference in the locations where these crashes occurred (Figures 4 and 5). These figures clearly indicate the following:
* Cities with higher crash rates have a higher proportion of crashes on roads that have four or more lanes.
* Cities with higher crash rates seem to have more crashes at mid-block.
Location of Fatal Crashes on Different Road Widths in US Cities Selected Randomly for Low and High Crash Rates
Location of Fatal Crashes, Junction or Mid-block, US Cities Selected Randomly for Low and High Crash Rates
The data from these cities confirm that higher fatality rate cities have a greater proportion of crashes on wide roads and at mid-blocks. The results suggest that average speeds could be higher in the high accident rate cities. Further, whether the higher proportion of crashes are due to higher percent of wide roads or other city characteristics that encourage higher speeds by their very form and structure. One possible reason for a higher proportion of crashes at mid-block could be that the average distance between junctions is higher, allowing motorists to reach higher speeds mid-block.
The fact that there is a difference in the location of crashes between the high and low fatality rate cities in the US suggests that urban form and street design influences average vehicle speeds in the city. This needs to be further investigated with road and street design details of these cities.
Major differences in fatality rates for cities around the world and for those within the US are also observed in India. Interestingly, the distribution for Indian cities is similar to that in the US – there are greater differences in cities with a smaller population than those with large populations. In the absence of more detailed information about Indian cities, it is not possible to investigate the factors associated with these differences. It does, however, appear that ‘culture’ does not play a determining role in explaining the difference in rates.
Other investigators have used models to assess the effect of street and street network characteristics on total crashes, severe injury crashes, and fatal crashes.3 They used data from over 230,000 crashes that took place over 11 years in 24 cities in California at the US Census Block Group level of geography. The results suggest that denser street networks with higher intersection counts per area are associated with fewer crashes across all severity levels. Conversely, increased street connectivity as well as additional travel lanes along the major streets went along with more crashes. Also more lanes resulted in an increase to the expected number of crashes across all severity levels. The average total number of lanes on the citywide streets had a higher levels of statistical significance with respect to safety of all the variables in their dataset. A higher percentage of citywide streets with raised or painted medians was significantly related to increasing overall crash totals and severe injury crashes. However, it is possible that the presence of medians was also associated with the presence of wider streets. Having bike lanes along the citywide streets was associated with a decrease in the expected number of fatal crashes.
Marshall and Garrick’s results for a limited number of cities in California reflect what our results for all US cities indicate using a different method. Therefore, it is reasonable to assume that wider roads with long block lengths was associated with higher crash rates in cities. We also know that improvements in crashworthiness of vehicles, use of seat belts and airbags and other safety devices can reduce fatality rates by 30-70%, alcohol control about 30%-40%,4 and that enhancement in road and infrastructure facilities can lead to an increase in fatalities. But, the differences in rates across cities in US and Europe indicate a difference by a factor of three or more. This suggests that city structure, modal share split, and extent of exposure of motorists and pedestrians may have a greater role in determining fatality rates than vehicle and road design alone.
If it is not easy for city residents to walk, bicycle or use public transport, then they will prefer the use of private modes of transport. When a majority of commuters are dependent on motor vehicle use for their essential needs, the system creates a political demand for greater provision of motor vehicle facilities and road space. This in turn can make it difficult for the political system to be harsh on drivers in terms of speed enforcement and controlling drinking and driving. In this situation, not only do people tend to use a motor vehicle for short trips, but also demand facilities that reduce trip time for long trips. These conditions serve to increase exposure of people on roads with less than optimal conditions for ensuring road safety.
Most cities around the world face serious problems of inadequate mobility and access, vehicular pollution and road traffic crashes and crime on their streets. An increase in the use of cars and motorized two-wheelers add to these problems, and this trend is not abating anywhere. It is expected that improvements in public transport can help substantially in alleviating some of these problems. However, modern cities, especially in low and middle income countries, have mixed land use patterns, a large proportion of all trips are walk or bicycle trips, and of the motorized trips, more than 50% are by public transport or shared paratransit modes. Deaths and injuries due to road traffic crashes are also a serious problem in these cities.
Walking and bicycling are the only clean modes of transport available. Their use tends to reduce as incomes rise and cities become unfriendly to these modes when roads are designed with motor vehicles as a priority. The high risk of injury and fatalities in urban areas to pedestrians, bicyclists and commuters in access trips has been documented from all over the world. Unless walking, bicycling and access to public transport is made safer, it will be difficult to promote these modes.
The data presented in this study show that:
* Fatality rates in cities are not determined solely by income levels or city size. Fatality rates among cities with similar incomes or similar population levels can vary by a factor of 3-5. This indicates that city street structure and urban form has a significant effect on fatality rates, over and above issues of vehicle design and enforcement.
* Cities with a higher proportion of wide streets and low density road networks appear to have a much higher fatality rate.
* Urban form and street design patterns may have to be given greater importance to improve safety of pedestrians, bicyclists and transit users.
* The built environment has a strong influence on both people’s subjective perception of safety and objective safety indices. A move towards designing safer streets and neighbourhoods has to become an integral part of our efforts to move toward a more sustainable future.
There are other issues associated with provision of wide high speed roads inside cities. For example, few people are aware that children living on wide noisy roads tend to do less well in school than those who live in quieter neighbourhoods, all else being equal.5 In addition, children living on wide busy roads tend to have much fewer friends than those living on streets with less traffic.6 The effect on the elderly is similar. Senior citizens are reported to live lonelier lives on wide, busy and noisy streets and suffer greater health problems with elevated blood pressure, and so on. This is partly because they cannot easily cross the street and thus lose half the population for socialization, shopping and other human needs.
Elimination of wide and elevated transportation corridors reduces noise and pollution and makes a city more liveable. Statistical data from many cities shows that rental prices for residential accommodation have a distinct relationship with noise levels – noisier streets have lower rentals than less noisy ones. This is why many residents occupying prestigious plots in our cities shift out when the road in front of their homes is widened. Their residences end up as commercial establishments, legally or illegally.
It appears that we should avoid building any urban artery more than 45 m wide, of which not more than 25 m should be available for motorized traffic and the rest devoted to bicycle and pedestrian paths, the tree line etc. This is because pedestrians cannot walk more than 25 m in one pedestrian phase of the traffic signal cycle. To ensure maximum speeds lower than 50 km/h it helps to maintain block sizes around 600-800m square. Smaller block sizes also ensure smaller walk distances to bus stops. At present all our urban development policies are following outmoded practices of the 1950s and are absolutely out of sync with current thinking on these issues.
We must spend more time in understanding the role of urban design and its influence on traffic safety. Once we are able to design safer cities, we can then promote cleaner modes of travel more easily. Therefore, urban safety also becomes a necessary condition for control of global warming.
* This work was partially funded by the Volvo Research and Educational Foundation.
Professor Shrikant I. Bangdiwala (University of North Carolina, Chapel Hill) provided support for statistical analysis. Aishwarya V. Chaturvedi assisted in data collection.
1. NCRB, Accidental Deaths and Suicides in India – 2011. National Crime Records Bureau, Ministry of Home Affairs, New Delhi, 2012.
2. Margie Peden, R. Scurfield, D. Sleet, D. Mohan, A.A. Hyder, E. Jarawan and C. Mathers, World Report on Road Traffic Injury Prevention. World Health Organization, Geneva, 2004.
3. W.E. Marshall and N.W. Garrick, ‘Does Street Network Design Affect Traffic Safety?’ Accident Analysis and Prevention 43(3), 2011, pp. 769-781.
4. Op cit., fn. 2.
5. C. Dora and M. Phillips, Transport, Environment and Health. WHO Regional Office for Europe, Copenhagen, 2000.
6. D. Appleyard, M.S. Gerson and M. Lintell, Livable Streets. University of California Press, Berkeley, CA, 1981.