Tuesday, July 12, 2011

Traffic Signal Treatments in the CROW Manual

The CROW Manual is written to describe measures that will make cycling irresistible.
Here's the list of treatments and selective text taken from the Manual that I copied down while listening to a lecture by Peter Furth. The "V" is used in the Manual to identify where there is a sketch in the back of the document.

Traffic lights - Page 203 - Section
Criteria and design requirements
Location of traffic lights
Flow capacity
Waiting time and chance of stopping

Cycle time
Preferably not longer than 90 seconds. 120 s for motorized traffic is too long for cyclists.

Subconflicts between motor vehicle and bicycle
Cycle track, cycle lane, or combine cyclists with other traffic
Three main movements can be distinguished for cyclists at an intersection: they turn right, they ride straight on, or they turn left. The choice of type of bicycle facility on a controlled intersection depends on the bicyle facilities present on the approach roads, the existence of subconflicts and the motorized traffic intensities that occur.

Cyclists turn right V47, 48
At an intersection with traffic lights, delays for cyclists turning right can be limited by leading these cyclists around the provision (right turn past red) or if necessary by permitting ‘right turn through red’. In that case, cyclists turning right must not be hindered by cyclists riding straight ahead (and vice versa). Attention must also be paid to cyclists merging (use protected are, if necessary).
V49 If neither ‘right turn past red’ or ‘right turn through red’ are possible then the stacking space for the cyclists is important. Cyclists who are stacked in front of a red light with the intention of turning right must not hinder cyclists proceeding straight ahead or turning left. To increase the flexibility of the provision, it may be desirable for cyclists turning right to be allocated their own signal group. IN that case it is desirable that they have their own stacking lane.

Treatments for "Cycles ride straight on" V 50
With a combined profile

Treatments for Cyclists that turn left V51, 52, 53

The Manual goes on to identify "Maximum waiting time for motorized traffic."
Naturally, the criteria for the flow of motorized traffic should also be considered together with the criteria and design requirements for bicycle-friendly traffic control systems. The quality requirements for motorized traffic also determine the options of shortening waiting times for bicycle traffic. In general, an average waiting time of 60 s and a maximum waiting time of 120 s is used for motorized traffic.

Policy and management
One of the most significant improvement options for bicycle traffic in traffic lights control systems is at the level of policy development, or more concretely, in the formulation of clear basic policy principles. Experience has shown that many traffic light provisions are created by a traffic control engineer with a large degree of independence. Taking account of the interest of all traffic participants and based on their own knowledge and expertise, engineers create a traffic control system that is always a ‘compromise’. Such an approach means that the control engineer has a significant influence on traffic policy of the road management authority concerned.

In order to avoid this ( I guess they assume Dutch signal engineers aren't designing for cyclists?), but also so as not to leave such dilemmas to the engineer during the design process, road management authorities responsible for various traffic control systems should develop ‘TCS policy’. (We wrote about this in the Signal Timing Manual's Chapter 2, but not specifically with bikes in mind). This should state what priorities are assigned to the various categories of traffic participants in the various road situations. A basic principle that can be applied is that (sections with) main cycle routes have right of way at intersections inside the built-up area. It is also possible to indicate maximum values for waiting or cycle times. If such basic principles are recorded in administrative regulations, the control engineer has very clear goals, which can also be tested easily.

(We have now started this in Portland with our half signals)

In many situations, current practice often results in unnecessary and unnecessarily long waiting times for cyclists, without this having any basis in policy. Research has shown that at almost all intersections where waiting time for cyclists were judged to be unacceptable this was the result of priority for other traffic (green waves or priority to public transport); in most cases, this was not based on adopted policy (even in the Netherlands).

Another important measure is carrying out regular maintenance of the control system. Once a traffic control system is up and running, it is all too often neglected. Carrying out regular maintenance and checking on the street to see whether specifications are still satisfactory helps to ensure that a system is optimally adjusted to the traffic situation.

Options for bicycle friendly provisions V 54 to 67, 76 & 77
The facility sheets of this Design Manual contain many measures to improve the situation for cyclists at intersections with traffic lights. A large number of these measures concern shortening the waiting time for cyclists. A minimum waiting time is essential for bicycle-friendly control. The various measures can be implemented individually, but often also in combination (see table 26). The effects of the various options can differ from situation to situation. Consequently, every situation must be thoroughly analyzed to determine the most appropriate measures.

Now if only the MUTCD was more like this.

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