When the new Golden Gate Bridge barrier opened, it was heralded as a new age of safety, but there were rumblings of problems immediately. Bridge Manager Kary Witt was quoted as saying, “I do think everyone is driving too fast. Everyone needs to slow down." A few days later, he was rather more forceful: “We're seeing too many drivers driving 20 to 30 miles over the speed limit. It’s completely unacceptable.” While the district seems to have been caught off-guard, this was an entirely predictable result.

Keeping roads safe is one of the most important tasks traffic engineers have. To do this, they will often try to improve a road’s safety by making it more forgiving of driver error: make the lanes wider, smooth out the curves, remove trees, and add median barriers. But this sort of improvement assumes that people drive a set way without regard to their environment.

This is not true. People drive as fast as feels safe, and they subconsciously react to visual cues to tell them what that speed is. Have you ever driven along a road at what felt like a comfortable speed, only to find that you were going 55 in a 35 zone? You were a victim of this subconscious pressure, called risk compensation.

By removing dangerous obstacles, engineers will often paradoxically make a road less safe by encouraging higher speeds. In a limited-access highway this might be okay, but on roadways that aren’t limited access – like the Golden Gate Bridge – it can create a dangerous false sense of security.

This is precisely what is happening on the bridge. Before, drivers on the bridge had a very visible cue that danger was omnipresent as traffic whizzed by in the opposite direction just a foot away. People would drive slower to ensure they had control of their vehicle and wouldn’t accidentally drift into traffic. They also had to navigate the very tight space between toll booths, slowing traffic further.

By removing the toll booths and adding the center barrier, the bridge district has lowered the perceived danger of crossing the bridge. This has encouraged drivers to drive faster, which has resulted in more crashes.

This is not a limited access roadway, either. There are driveway entrances and exits at the Toll Plaza and at Vista Point. Pedestrians and bicyclists cross the bridge on its sidewalks. This is a recipe for disaster.

It is perhaps understandable that the district would choose to spend millions on a median barrier. It was a harrowing crossing, and I know I never drove in the left lane if I could avoid it. But it is baffling that the bridge district was apparently unprepared for higher speeds as a result of this change.

There is a lesson here: traffic speed follows design. If towns and cities in Marin want to reduce speeds and increase safety, it must design roads that encourage people to follow the desired speed. The Golden Gate Bridge District has done the opposite, telling people to go one speed while silently encouraging them to go faster. If it’s serious about keeping speeds down, it won’t rely simply on enforcement to keep speeds down but will also seek design solutions.