Clarendon Cycles: Getting the Right-of-Way Right

One of the basic principles of road design and traffic management is that — at intersections, at least — bigger roads trump smaller roads. Streets with higher traffic get priority over less-travelled roads. This is why, for example, the lights on Glebe Road are generally set to accommodate the traffic travelling the length of Glebe and not the traffic trying to cross it. The idea is that priority is given to what benefits the most people. It’s just common sense, some would say.

Perhaps, then, we should consider applying that principle to the Custis Trail in Arlington.

Thanks to Arlington County’s trail counters, we know that thousands of people a day use the Custis to commute. Unfortunately, we also know that several of the intersections with streets near the eastern end of the Custis are frequently the site of bike-car crashes. I suspect that if we adopted similar prioritization approaches for the Custis Trail street intersections, we could reduce the number of crashes at these crossings.

The existing prioritization approach is one reason there’s no easy solution for the most dangerous of these intersections — where the Custis crosses Lynn Street, parallel to Lee Highway. While simply prohibiting a right on red would go a long way to reducing bike-car conflicts, the state Department of Transportation prioritizes the turning movement of the massive volume of vehicles exiting Interstate 66 over the safety of the fewer users of the Custis Trail.

At some of the Custis intersections with streets just west of Lynn, on the other hand, the traffic situation is just the opposite. While I don’t have any traffic count numbers for it, I’m certain the automoble traffic on Quinn Street, for example, is but a small fraction of the bike traffic on the Custis Trail.

Yet the Custis-Quinn intersection is still designed in such a way that cars coming from Quinn have effective priority over trail traffic, which is expected to stop before proceeding through the intersection.

This is in direct contravention to the basic prioritization principle. It’s as if someone were to put up stop signs along Lee Highway at every side street, requiring Lee Highway traffic to stop regardless of whether any cross traffic was present. In addition to being inefficient in terms of traffic throughput, the constant stopping and starting would certainly raise the frequency of crashes.

So why don’t we prioritize the Custis Trail traffic over the traffic on lesser-used streets like Quinn? In practice, this could mean raising the pavement so that the trail had a clear and continuous path across the intersection. Quinn Street traffic would be faced with a prominent sign noting that cross traffic does not stop. That’s just my amateur engineering – I’m certain that professionals could accomplish such a prioritization safely.

By making it clear that bikes have priority and will not be stopping, drivers would be less apt to roll past the stop sign without looking for bike traffic, as they frequently do now. It would also reduce the chance of bike-on-bike crashes caused when one cyclist stops but the one behind him or her only expects that person to slow.

This isn’t a proposal I make lightly, and I recognize that even though it’s based on a well-established principle of traffic design and engineering, it requires a bit of innovation on the part of Arlington County’s transportation officials.

But Arlington’s already taking a leadership role in developing and implementing traffic controls that accommodate all forms of transportation, and this could be another step in that direction.

It’s the sort of thing a Gold-level Bicycling Friendly Community might do, no? I hope Arlington County will take a closer look at this way of making our streets and trails safer.

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Here's an example of a trail-street intersection along the Detroit Greenway in which trail traffic is given priority over a lesser traveled street. Not shown is that the stop sign has a flashing border, alerting drivers to a special traffic situation.

WashCycle has a good post about a proposal — not plans — for improvements to the eastern end of the Custis Trail.

Hey, look who's getting some on-street bike parking? Good move, Arlington.

The District Department of Transportation in Washington just released some of its own bike count analysis. I hope they follow Arlington's lead and install year-round automatic counters.

Mark Blacknell is a member of the Arlington Bicycle Advisory Committee, president of the Washington Area Bicyclist Association, and a League Cycling Instructor.