Ask R. Moses: Does Center Line Striping Make Streets Safer?
Today's question:
“A number of residential streets in my city have gone from having no striping to having a dashed yellow and sometimes having full solid double yellow striping. Before the striping on many of these streets, people seemed to drive slower. After dashed or solid yellow were introduced it not only seems people drive faster but there seems to be more traffic as the striping seems to suggest to drivers that the street is a through route.
To make matters worse, drivers now also seem to be more aggressive when overtaking bicyclists who are now considered to be “in the way” or in the “middle of the lane” compared to before when there was no striping.
A local engineer told me striping was supposed to make the street safer, but it feels like it has had the opposite effect. Is there any evidence to suggest that striping a center line on residential streets actually improves safety or slows drivers down?”
R. Moses' Answer:
More than anything else, line striping is a flag. It is a flag that denotes “my” territory from “your” territory. When streets do not have any striping, especially in residential or recreational areas, they are generally understood by most to be common areas. Drivers should not be surprised to find kids playing ball, people walking or riding bikes, or parked vehicles within the roadway space, which may force the driver to use the entire width of the road to navigate around all these other legitimate uses for streets in residential and recreational areas.
But the second line striping is painted, the general perception is that the roadway real estate has been “assigned” to a particular variety of user, and users are more likely to become agitated or more aggressive when “others” infringe on “their” territory. It also stands to reason that if a driver feels that a certain corridor within the street is “theirs” and other users should not be there, they will then be more comfortable increasing their travel speed. And yes, providing lane striping also provides a visual cue that the street is expected to be used as a through street. And if it actually does attract new through vehicles, average travel speeds will almost certainly rise, as it is well known that people will drive through other neighborhoods faster than they drive through their own.
Streets without any road striping create an environment where there is some ambiguity on who should be where, and I believe this encourages lower speeds and more caution on the part of drivers. There is limited hard research on this topic, but what is available supports this concept. Center lines may make it safer for cars to avoid head-on collisions at night time, but these are not common on low volume residential streets. Center lines are fully optional (per MUTCD) for streets with traffic volumes of less than 6,000 per day, and most residential streets have volumes well below this mark.
At one time I lived on a residential street that was often used to bypass a stoplight on the major streets. We often met with neighbors in the street and held block parties and events in part to discourage people from using it, and to slow them down if they did. I suspect that law enforcement might be against such things if the road were striped as it would be looked on more as a place for vehicles than people.
Now, striping can also be used for good. In another neighborhood where I used to live, the city stepped in and used striping to create a wide shoulder and narrow traffic lanes in some of these street. The wide shoulder became a de facto bike lane where previously it had been a weave in and out lane for taxis. Traffic calming in this way is also a lot cheaper than other traffic calming techniques like installing planter barriers or concreting the street up to sidewalk height at intersections. However, it sounds like the center lane striping in your neighborhood is not having that effect.
I discourage cities from adding lane striping unless the character of the street and characteristics of travel on the street indicates that such “assignments” would truly serve the common good.
How would you respond to this question? Jump in with your answers in the comments!
Note: R. Moses is not meant to be professional engineering advice nor should be relied upon as such. Consult your own technical professional before proceeding with your own project.