Comments on: Urban planning’s black eye

By: Martin Cassini

Martin Cassini — Tue, 22 Jun 2010 10:10:48 +0000

Nifty articles. As a student of the subject, I advocate treating the cancer at the heart of the system: priority based on status of road or direction of travel. Why do we have lights? To break the priority streams of traffic. Remove priority, and you remove the “need” for lights and the need for speed, enabling everyone to do what is civilised and efficient: approach carefully and filter. Could it be that simple? It could. In the US, you have the all-way yield. I refer to it as filter in turn. More at “FiT Roads” and “Free to Choose Free to Move”.

By: Lakers Parade Impact …

Lakers Parade Impact … — Mon, 21 Jun 2010 19:59:42 +0000

[…] Urban Planning’s Black Eye (Traffic engineers use traffic lights far too often when a simple stop sign works better and is much less expensive)Daily Journal Of Commerce – Oregon […]

By: Michael Patrick

Michael Patrick — Mon, 21 Jun 2010 16:17:21 +0000

How about TWYC? Two-way yield control? Often a full stop is inefficient and just not necessary, and slowing to look each way will do. All drivers are supposed to know what a yield sign means — yield to traffic with the right-of-way, including stopping when necessary — so using yield signs instead of stop signs should not pose any more safety hazard than stop signs.

By: Andy B

Andy B — Sat, 19 Jun 2010 12:16:36 +0000

Instead of assuming the choice is between AWSC/TWSC or signals, enter roundabouts into the equation. Many states have “roundabout first” policies because of their many advantages over signals, not the least of which is the dramatic reduction in crashes. “Roundabout first” simply means that planners/engineers improve a congested or dangerous (or both) intersection by installing a roundabout unless there is overwhelming, documented data showing it is not feasible.

The next time you hear a traffic engineer insist that a corridor has to be widened, left turns added, etc., ask how a roundabout would operate.

By: Doug Kelbaugh

Doug Kelbaugh — Sat, 19 Jun 2010 05:48:49 +0000

Arrol has clearly explained the advantages of 2 way and 4 way stop signs, which seem sensible, proven and intuitive.
What’s not intuitive or obvious is at what traffic flow traffic signals make more sense.
Can you or someone provide the figure – in ADT or vehicles/hour – when a single phase traffic signal is better?
And when a mult-phase signal (with the dreaded left turn lane or lanes) makes sense?
Thanks.

By: Christopher Neal Wyatt

Christopher Neal Wyatt — Sat, 19 Jun 2010 04:28:28 +0000

Every day I drive through an intersection south of Dayton, Ohio which has recently been retrofitted as a ‘continuous flow’ interchange, which features no less than 16 separate traffic signal installations.

The main innovation of this new type of interchange seems to be requiring all turning vehicles to wait at two separate sets of signals before completing their turns, ostensibly to ensure ‘continuous flow’ as left-turning and straight-traveling vehicles are separated into parallel channels, on the approaches to the junction. Even making a right turn at this new “continuous flow” junction entails waiting at 2 separate sets of signals!

I don’t think traffic signals are necessarily bad in and of themselves– they can actually be very useful, for example, by stopping traffic flow to allow pedestrians to cross a busy street. However, they are over-relied upon by the traffic engineering community, and by the looks of things in Dayton, we haven’t yet learned from this mistake.