Comments on: A Speed Nudge?

By: bikeolounger

bikeolounger — Tue, 30 Jun 2009 16:32:45 +0000

Yep, people speed often in areas where the lights are synchronized. I see it daily on my commute. Often, though, if it’s a grid of one-way streets, there are enough lanes that the real hot-dogs stay in one lane, allowing those who “get” synchronized lights to pass merrily along.

It would be cool to see the sync speed come down to about 20, allowing bicyclists to get further per light cycle, especially if there is one of those pesky bike lanes from which we can taunt the motorists (by simply being there–not actively taunting). We are trying to get this to happen locally, if not to 20, then to 25 or 28 from 35.

By: aaron

aaron — Sat, 27 Jun 2009 16:04:26 +0000

That’s another problem; rate of acceleration.

Engineers assume a slow rate because they can’t tell people how bad slow acceleration is, but policy makers could be working on getting acceleration rates up. That would greatly improve speed and light timing, fuel efficiency, drive times, and possibly safety.

By: aaron

aaron — Sat, 27 Jun 2009 15:58:51 +0000

(PMT, I meant Pedestrian Mile Traveled, but Passanger Miles Traveled should also be looked, rather than just VMT. Of couse, payload value miles traveled should be considered too.)

By: aaron

aaron — Sat, 27 Jun 2009 15:56:49 +0000

Ed, I need numbers and data. Pedestrian and vehicle volume and travel distances.

The road pictured doesn’t look like one that would have increased ped incididents with higher speeds.

I think it’s mostly BS. 28 is still pretty damn fast for a pedestrian impact and I doubt it decreases the rate per VMT and PMT. Probably increases it.

By: Mark Young

Mark Young — Fri, 26 Jun 2009 17:13:09 +0000

Catching a ‘green wave’ has safety and environmental benefits (not just fuel efficiency, but also local pollutants from all the stopping), so – notwithstanding all the traffic modelling issues discussed here – this one has my support.

These kinds of ideas can be taken further, too – I was at a standards meeting recently where they were discussing new in-car telematics systems that give you timers on when the lights are going to change (you might have seen similar things actually on the traffic lights in some countries in Asia). This was mooted as a way of ‘nudging’ drivers to slow down early if the lights were about to change red – but I bet them any money that if drivers had that sort of info, they’d speed up rather than slow down.

By: Ed

Ed — Thu, 25 Jun 2009 18:31:49 +0000

@aaron, there is a huge safety benefit to a pedestrian of 28mph traffic versus 35-40mph traffic.

By: Allan

Allan — Thu, 25 Jun 2009 17:39:05 +0000

What about this: you turn onto the street and just make a yellow. you can then speed up to like 40 and get progressively earlier in the green. Assuming this is a grid and you are going diagonally, you can turn right at the beginning of the green and then gun it to make the next set of lights. you have defeated the speeds

By: Kenneth Todd

Kenneth Todd — Thu, 25 Jun 2009 14:19:22 +0000

The idea that better traffic signal synchronization will reduce travel time and relieve congestion is very attractive and easily sold to the public. Drivers always hope to hit green at the next light.
That’s why the experts extol the wonders of synchronized traffic signals but forget to give us the bad news. These systems function only with moderate traffic volumes and usually in one direction only. Those who travel in the opposite direction and on the side streets pay for it with longer delays. That’s why they measure the savings of time and fuel only on the road where the traffic signals are synchronized.
But when there are more vehicles than fit through the green, some are left behind to wait for the next green and the next bunch has to stop till they are cleared. And when a driver turns into the coordinated flow from a side street,
he gets to the next light when it shows red, so that the next bunch again gets stopped by a stationary vehicle. Only when we are lucky do we get faster to the next bottleneck, where we have to wait that much longer.

By: gpsman

gpsman — Wed, 24 Jun 2009 20:10:29 +0000

“If, upon getting a green, if drivers knew that driving 28 mph would get them to the next light when it was going to change, and that to go faster would simply cause them to have to come to another stop, would they actually drive at that speed?”

Probably not, unless the timing incorporates the average rate of acceleration from a stop to 28mph, probably around 2-3 seconds.

Third St. in downtown Cincinnati (SL 25) lights are timed at about 18-20 mph, including a rather slow rate of acceleration. Leave first at the light, drive 18-20 mph and traffic will pass, change lanes to your front and fill up that space with 6-10 vehicles within a block (catching the red, of course) leading the light-timer to have to stop, and then, of course, to miss a downstream green they are attempting to time.

Practically nobody is willing to spare their time to compare the feeling/s of velocity against actual results. Apparently, progress is very often measured by only vehicles passed.

By: aaron

aaron — Tue, 23 Jun 2009 17:37:58 +0000

The effectiveness studies Information Display Company uses to sell it’s products (do not focus on efficiency, these systems are sold as safety products, and are not related to the speed/stop light coordination system), do not show any improvement in safety. They only evaluate effectiveness in reducing speeds (reducing fuel efficiency, time efficiency).

http://www.informationdisplay.com/docs/effectiveness_studies_022509.pdf

The only evaluation that even mentions safety, suggests that it does not improve safety. This CHP Memorandum is from IDC effectiveness studies document (emphasis added):

Memorandum

Date: February 2, 2007

To: Humboldt Area

From: DEPARTMENT OF CALIFORNIA HIGHWAY PATROL
Humboldt Area

File No.: 125.11998

Subject: REDUCTION OF COLLISIONS ASSOCIATED WITH ROADWAY CHANGES IN THREE AREAS OF HUMBOLDT COUNT

In 2006, there was a significant reduction of collisions at three locations in the Humboldt Area. The reduction of collisions was associated with engineering changes made by the California Department of Transportation (Cal Trans). These changes include changing the roadway surface from conventional asphalt/concrete pavement to “opengrade” asphalt/concrete pavement and posting additional sings, some of which are radar activated signs that indicate the speed of approaching motorists. Two of these areas are located on US 101; the third area is located on SR-299.

The north most area is located on US 101, between mile post markers 101 HUM 124.71 and 125.98; a stretch of highway frequently referred to as “the curves just south of the by-pass, north of the old fish hatchery.” In 2004, there were nine reported collisions in this area. In 2005, there were eight reported collisions in this area. Cal Trans completed a safety project, which included a change to “Open Grade” roadway safety surface, and the addition of radar activated signs in December 2005. In 2006, there were 5 reported collisions in this area.

The second area on US 101 is located between milepost markers 101 HUM 109.42 and 112.53; an area commonly called “the Big Lagoon Curves.” In 2004, there were 12 reported collisions in this area. In 2005, there were also 12 reported collisions in this area. Cal Trans completed a safety project in this area that included radar activated signs and a change to “open grade” roadway surface in December of 2005. In 2006, there were 5 reported collisions in this area.

The third area is located on SR-299 on the east slope of Lord Ellis Summit, between milepost markers 299 HUM 19.05 and 20.67. Though the curves are not as tight as those on US 101 are, the roadway grade is steep. Both in 2004 and 2005 there were 12 reported collisions in this area. Though no comprehensive safety project was conducted in this area, Cal Trans conducted a number of incidental improvements and repairs. This area does not have radar activated signs. In 2006 there were three reported collisions in this area.