Q: I believe that studies show after changing an
intersection to a roundabout, there will be more crashes in the roundabout than
an intersection but the crashes will be less serious in the roundabout. Could
there be a similar phenomena concerning side roads and expressways? For
example, if I travel from Fairhaven to the airport, would I be more apt to have
a collision if I took side roads than if I took I-5, but if I had a crash on a
side road, would it probably be less severe than if I had one on the
expressway?
A: You’re 83 percent correct about the studies on
roundabouts and collisions (and I just made up that percentage). But the
following percentages were determined by actual researchers: A national study by the
Insurance Institute for Highway Safety found that roundabouts decrease
fatal crashes by 90 percent, injury crashes by 75 percent, pedestrian collisions
by 40 percent, and overall crashes by 37 percent. However, those studies focused
primarily on single lane roundabouts.
The same organization studied our
first two two-lane roundabouts on Guide Meridian and found that serious
crashes were similarly reduced, but there was an increase in crashes that only
resulted in property damage. The study was done in the year after the roundabouts
were installed, when many drivers using them were still unfamiliar with how to
navigate them properly. The researchers suspect that because two lane
roundabouts are more complicated than single lane roundabouts, confusion and
lack of experience may have been a contributing factor to the increase in
non-injury crashes.
As for other possible reasons for the increases,
a study
in Wisconsin found that a significant number of roundabout crashes were
caused by drivers running off the road. Some drivers would speed up when
entering the roundabout, apparently searching for the thrill associated with
high-speed cornering, and end up leaving the roundabout too soon. The same
study also noted a high percentage of crashes involving impaired drivers,
indicating that it’s hard to drive in a circle when you’re drunk.
But this isn’t an article about roundabouts; we’re
trying to answer the question of whether it’s safer to drive on side streets or
the interstate. If we just look at raw numbers, the interstate is the way to
go. Taking 2017 as an example, of the 565 fatalities that year 91 of them were
on a limited-access freeway, while the rest were on city, county and state
roads. But in this case, raw numbers aren’t that helpful because we have a lot
more city, county and state roads than freeways in Washington.
We’d get a better comparison by looking at not
only fatal crashes by road type, but also miles traveled. Fortunately for us,
the Federal
Highway Administration keeps track of that sort of thing. Their report
sorts miles traveled into seven different road types. For the sake of this
discussion, I’ve aggregated them into either freeway or non-freeway. In 2017
drivers in Washington traveled over 61.4 billion miles. About 24.9 billion of
those miles were on freeways; the remaining 36.5 billion were on non-freeway
roads.
This whole thing is about to get nerdy, but stay
with me. If you do the math, we get .37 fatalities per 100 million miles
traveled on freeways and 1.3 fatalities per 100 million miles traveled on
non-freeways. In Washington we have about three-and-a-half times more fatal crashes
per 100 million miles traveled on local, collector and arterial roads compared
to freeways. To break it down further, rural minor collector roads have the
highest fatality rate, at 2.3 fatalities per 100 million miles, so if you’re
planning your route for safety those would be the roads to avoid.
Why are roads with a speed limit of 60 or 70 mph safer than roads with 25 to 55 mph speed limits? I’ll propose a few reasons: It’s hard to have a head-on or right angle crash on the freeway, but they’re more common in intersections (127 intersection fatalities in 2017) and you won’t be able to use side streets without going through some intersections. Also, run-off-the-roadway crashes resulted in 194 fatalities in 2017, and while you can run off the road on both a freeway and a side street, the distance between the fog line and the closest immovable object is generally a lot farther away on a freeway. Shoulders that are as wide as another lane, along with wide patches of grass beyond the shoulders help to mitigate the consequences of running off the freeway, while on side streets you’ll find telephone poles and buildings mere feet away from the traffic lane. Finally, a driver has to identify and react to a more diverse set of circumstances on local roads; intersecting roads and vehicles coming from multiple directions, along with cyclists and pedestrians. This creates more opportunities to make a mistake. And while speeds are slower on side streets, they’re still fast enough to have grave consequences.
Unless we return to the speed limits set in 1909 (12 mph in the city and 24 mph on rural roads, which coincidentally is about the speed that you’ll travel in a roundabout) the freeway will be the safer bet.