The City of Toronto plans to narrow lane widths to improve traffic safety. However, traffic-engineering experts believe that narrow lane widths are associated with higher accident rates.
While John Tory, the mayor-elect, has already endorsed the City's plans, he and the traffic experts at the City must review traffic safety studies that conclude otherwise.
A front-page story in the Globe and Mail reported that the city is exploring options to reduce road lane widths to improve traffic safety. City's traffic department believes that narrow lane widths will result in reduced speeds, which they think will improve traffic safety. Stephen Buckley, the general manager of the City's Transportation services department, told the Globe that lane widths in the downtown core in American cities are already down to 10-feet.
While the City's traffic department sounds confident in its assertions, its recommended guidelines on lane widths are in stark contradiction to what we know from traffic engineering and safety studies. Narrower lane widths by default have higher accident rates. Even more disconcerting is the City's backgrounder on lane width guidelines, which states that traffic "throughput is independent of speed." Nothing could be more wrong about traffic flow than this statement.
I had the privilege of studying under Professor Emeritus Ezra Hauer, who is a world-renowned expert on traffic safety. In a paper addressing lane widths, Prof. Hauer wrote: "under identical traffic conditions, roads with 10 foot lanes have 5% more crashes and roads with 12 foot lanes have 1% more crashes than roads with 11 foot lanes." He further explained that while 3-metre wide roads had more crashes than 3.75-metre wide roads, the difference between 3.65-metre and 3.75-metre roads was not significant.
Professor Hauer is not alone in raising concerns about narrow lane widths. Most traffic-engineering experts have concluded the same. In a paper published in 2014 in the journal Safety Science, the University of Alberta's academics found a statistically significant and negative correlation between lane widths and accident rates. They explain the reasons why wider lanes are safer than narrower lanes. "Basic engineering knowledge suggests that wider lanes contribute to safer transportation facilities" because "any action that makes a task easier to perform will make that task safer to perform." Remember, wider lanes make it easier to drive and hence improve traffic safety.
There are even gender dimensions to this issue. A study published in Accident Analysis and Prevention concluded that that women were likely to experience more accidents than male drivers in "heavy traffic volume, reduced median widths, narrow lane widths, and large number of lanes."
It is important to note that some published research concluded that wider lanes increase accident frequency. Individuals, who are not traffic engineering experts, have usually authored such studies. Consider, for example, a study by Prof. Reid Ewing and Eric Dumbaugh in which they argue that accidents increase "as lanes exceed 11 feet in width." The authors, unfortunately, have misread and misquoted Prof. Ezra Hauer's research that concluded exactly the opposite.
Toronto's traffic services department plans to exempt bus and transit routes from lane width reduction. The exemption is motivated by a concern about buses being wider than cars and hence the need for wider lanes. Just like public transit buses, fire engines, ambulances, and school buses are also wide-body vehicles, which are not restricted to operate on designated routes. Narrowing lane widths will influence the ambulatory response times in the downtown core.
It is important to recognize that downtown Toronto is not merely an employment hub, but also a hub for health care facilities. Most advanced trauma centres, birthing centres, specialized hospitals for women and children are located in downtown Toronto. Narrowing lane widths in and around downtown Toronto will worsen travel times and consequently increase access and egress times to and from the primary health care facilities.
The backgrounder on lane with guidelines states that traffic flow is independent of speed or lane widths. This is in contradiction of the fundamental equation of traffic flow, which states that throughput (traffic flow) is essentially a function of two variables, i.e. traffic density and speed. Narrow lane widths will lead to lower traffic speeds, which will reduce the traffic flow through the urban core.
The City's backgrounder on lane widths further states that regardless of their speed, cars maintain two second spacing between them. Again, the fundamental equation of traffic flow states that the spacing between vehicles increases with speed.
What concerns me even more is that the City's guidelines claim that reducing lane widths will not reduce traffic speeds or traffic flows. However, the City's traffic department gives a different message to the newspapers revealing that the purpose of lane width reduction is primarily to reduced traffic speeds. What is the logic behind issuing contradictory statements?
Traffic engineering offers a whole host of traffic calming solutions to lower speed on urban arterials. Accidents occurring at lower speeds have lower fatality rates than those at higher speeds. However, system-wide narrowing of lane widths is likely to worsen traffic safety in the City and not improve it.
Remember, the road to hell is paved with good intentions. Let us not be narrow-minded about lane widths.
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