Use traffic signals to meter or gate traffic to prevent congestion and cut emissions

Submitted by john on Sun, 15/12/2019 - 15:50
Wasted space

The purpose of metering is to prevent congestion. It is done by traffic signals limiting the flow to 90% of capacity. Then a green wave can be managed between successive intersections. Ideally this green wave is a platoon that moves at the speed limit, in a compact bunch without dispersing, and with a minimum of acceleration and braking. The time gap between the traffic platoons will be relatively clear of traffic, allowing easier access to side streets and properties. Then the outcomes are: minimum trip time; minimum CO2; minimum particulates; a reduction in associated noise; and easier access; that would all greatly improve the amenity of arterial streets.
Emissions are strongly related to average trip time. It is estimated that:
* 4,200 cars per hour currently congested, emit 12.5 tonne of CO2,
* 5,300 cars per hour when metered, would emit 13.2 tonne of CO2,
* but if 90% of the 5,300 jump the queue, only 5.9 tonne of CO2 would be emitted.
Emissions for the 4,200 are only slightly lower because of the current slower trip speed, despite the much less traffic volume. But queue jumping, by 90% of traffic when metered, drops CO2 emissions by an astonishing 53%! Jumping the queue is more important for emissions than capacity, and is presented later.

Any reduction in capacity will increase delays and the 10% reduction proposed for metering should be recovered, if not available by bus lane removal, then by converting at least the most critical intersection to two-phase (see later), either by banning right turns in the crudest and most immediate option, but preferably by installing right turn cross-overs on approaches. The crude banning of right turns will have less impact than the alternative congestion.
Highly valued trips made by community and business leaders, tradesmen, sales and deliveries are best made by private transport and constitute the most important and greatest quantity of traffic. They can not be avoided nor shifted to other modes without loss of value and they must be taken during the peak period. These trips warrant priority.
But to avoid congestion-delay to buses in Hoddle St, a bus lane has been reserved for them, reducing the capacity available to general traffic to 75% of its previous value. The bus lane has been very effective in removing delay to buses, but its side effect is an increase in the AM peak period delay by 15 minutes for 5,300 cars per hour, causing, 1,100 drivers to shift away from cars, mainly onto the bus, reducing the demand to 4,200 cars per hour, the existing state.
While the existing bus lane removes congestion-delay to buses, that benefit could also come from metering. And the green wave and smoothing at minor crossings with metering would also remove delays to buses caused by traffic signals, so metering is of greater benefit to buses than a bus lane. Smoothing is presented later. If the bus lane was replaced by metering, buses would have less delay, priority trips would save 15 minutes, capacity would increase by 20%, and the option of halving emissions and trip time by queue jumping becomes available.
In Hoddle St, modelling shows that 1,100 people chose to use the bus rather than cop the extra 15 minutes delay. It follows that buses were available to substitute for 20% of trips, and that 20% of people prefer to take the bus than to endure the congestion. That is their decision to make, and it is based on their low value of the cost of mode change. But getting rid of congestion can: save 90% of people 15 minutes each, assuming half the benefit for the 20%; improve amenity for residents; and reduce CO2 emissions by 53%. This is a demonstrated net benefit that would apply to some degree for all congested arterial streets. So to get rid of all congestion, anywhere, through metering, that costs only 10% of capacity, net benefits apply, and the benefits of green waves would apply for all vehicles, including buses. This thesis rejects the current practice of permitting congestion.
A bus lane was installed in Stud Rd, where there were only 5 buses per hour, and reduced its capacity by 33%. This created huge delays for the general traffic, and caused such a public reaction, that it had to be removed. A similar response is expected for the 3-lane section of Hoddle St and in the 3-lane Punt Rd section of the route, where there are only 5 buses per hour, and such a proposal would reduce the capacity of the road by 33%. But metering could be installed there on the basis of removing congestion, with the benefit of also providing priority for buses.
Metering has nothing to do with capacity nor tolls. It is simply using traffic signals to prevent congestion, and reduce emissions and trip time. All traffic can use any lane. Metering creates or retains a queue. Metering was successful for the Melbourne Commonwealth Games.

Metering is also described as signal control optimisation, the effects of metering can be measured, metering can cause political problems, but the opposite of removing bus lanes is equally an issue..