2.7Time settings#

2.7.1General#

The time settings listed following are set to the time settings determined by the Traffic Management Designer when the signals are installed on site.

In fixed-time and vehicle-actuated modes of operation, the times are selected manually for each site. In manual operation, the timings are manually controlled in each cycle.

2.7.2Yellow time#

The length of yellow time shall be four seconds for Type-1 PTSS. The length of yellow time for Type-2 PTSS may be increased from four seconds with consideration to the controlling factors. For guidance, refer to Austroads Guide to Traffic Management Part 9: Traffic Operations.

2.7.3All-red time#

The all-red time is the time period after one approach changes to red, and before the opposite approach changes to green.

The all-red time shall be long enough to allow a vehicle to pass the stop line, and safely clear the work zone while travelling at the speed limit. The all-red time varies according to the work zone length and the posted speed limit. (The work zone length is measured as the distance between the stop lines at each traffic signal unit.)

All-red times for various speeds and work zone lengths are shown in Table 2.7.1. The relationship between the all-red interval and travel distance for a range of vehicle speeds is also illustrated in AS4191.

For distances or speed limits other than those nominated in Table 2.7.3, the all-red time shall be calculated using the following formula:

𝑡𝑡𝑎𝑎𝑎𝑎= 3.6𝐿𝐿𝑐𝑐 𝑉𝑉𝑑𝑑

where

𝑡𝑡𝑎𝑎𝑎𝑎= 𝑎𝑎𝑎𝑎𝑎𝑎 𝑟𝑟𝑟𝑟𝑟𝑟 𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡 – 𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚 𝑏𝑏𝑏𝑏 𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒 𝑜𝑜𝑜𝑜 𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔 𝑡𝑡ℎ𝑎𝑎𝑎𝑎 1.0

𝐿𝐿𝑐𝑐 = 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠 𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙 (𝑚𝑚)

𝑉𝑉𝑑𝑑= 𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤 𝑧𝑧𝑧𝑧𝑧𝑧𝑧𝑧 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠 𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙

2.7.4Maximum green time#

The maximum green time varies with the two-way traffic flow and the work zone length.

Longer maximum green times may be used in vehicle-actuated operation, as the green time will only run to the maximum time where necessary. For fixed-time control, shorter green times are required. Unnecessary delays may occur if unsuitable green times are used.

Appropriate maximum green time values for both approaches may be selected from Table 2.7.4(a) (vehicle actuated operation) or Table 2.7.4(b) (fixed time operation).

The maximum green times for vehicle-actuated operation allows for some variation in traffic flow while ensuring a reasonable maximum cycle time. The actual cycle time for any cycle is dependent on the traffic demand, but the maximum cycle time shall always be less than 240 seconds.

The green times given in Table 2.7.4(b) were calculated (using aaSIDRA) to give the minimum practical cycle time with a degree of saturation less than 0.9. They assume traffic flows in each direction are equal. Allowance has been made for some peaking within the hourly volume and for 4% heavy vehicles.

Inter-green times for each work zone length were calculated by adding four seconds yellow time to the 40 km/h all-red times from Table 2.7.3.

These values are given as a starting point only. They are appropriate if traffic flows are similar in both directions and the two-way flow is known. The initial settings may be adjusted in accordance with Section 2.8.3 of this chapter. If long queues are regularly occurring on one approach, the maximum green time should be increased for that approach only. Manual operation may be used to provide traffic control if vehicle-actuated operation is not sufficient to clear the traffic.