Traffic Lights - Some Safety Aspects

Traffic lights have become so ubiquitous in our cities that many people have forgotten how many disadvantages they have. In fact, traffic light installation and timing involves many balances, almost all of safety versus convenience. One of these compromises involves the lengths of the amber signal and of the 'all-red' time. They have a significant effect on both traffic flow through an intersection and upon the accident rate at it.

It is a major offense under highway traffic acts to enter a light-controlled intersection after the light turns red. In Ontario, that means license demerit points and insurance rate increases. With reason - high-speed collisions from the side cause the worst injuries of all. Red Means Stop. But, to stop a moving vehicle takes time, so you must be given sufficient warning that the light is going to turn red, so you can stop safely before reaching the intersection. That is the purpose of the amber signal.

The warning time required has two parts. The first is the time required for you to recognize that action is required and to react with a physical movement, and the second is the time required for your vehicle to come to a full stop.

The Ministry of Transportation of Ontario (MTO) Ontario Traffic Manual (Book 12) recommends a driver reaction time of 1.0 seconds. (The branch says that they use 1.8 s for provincial highways - decisions are more difficult to make accurately at high speed.) It then adds a time based on a braking deceleration of 3 m/s² to get their recommended duration of amber signals:

posted speedamber timedecision distance
45 or less3.0

The provincial manual also recommends an all-red time sufficient for a vehicle 6 m long travelling at the posted speed limit to clear the intersection, for example 2.2 s for a 24 m wide intersection posted at 50 km/h. The provincial recommendations match those of the North American Institute of Traffic Engineers (ITE) Technical Council Committee 4A-16, except that the ITE recommends that actual speeds be used to calculate amber times, not posted speeds. Posted speeds are almost always slower, so in effect the ITE recommends longer amber times than the province does. It's a common delusion that lowering posted speeds will slow traffic. In fact, traffic travels at the speed most drivers perceive to be safe, which is determined by road design, not signs.

You should note that, if you are at the decision distance shown above, you can stop in time, but you will not complete the stop while the light is still amber - you will just complete the stop before you reach the intersection. If you require a deceleration of greater than 3 m/s² in order to stop prior to entering the intersection and keep going, you may be still within the intersection when the light turns red, but that is legal - you have the all-red time to clear the intersection as long as you maintain your speed. Either maintain your speed, or stop - no half way between.

The stopping capabilities required of new road vehicles in Canada are specified by Transport Canada (TC) in their Standard 105, which matches the US regulations under the auto pact between our countries. Table II of that standard shows the stop distances that vehicles under test must meet, under perfect road conditions with trained drivers, measured from the point at which the brakes are applied. When the numbers are matched up, the provincial recommendations match the federal requirements for heavy vehicles, and give passenger cars a reasonable leeway under clear-road conditions. But, there is not a word in the standard, the manual, or in the ITE recommendations, about allowances for rain-slick, snow or ice, nor is there a word about the limitations of pregnant, elderly or physically handicapped passengers. The law assumes that you will drive more slowly when any of these conditions apply.

However, most roads in Southern Ontario are now under municipal jurisdiction. There is no requirement that municipalities follow the provincial manual, and some do not. Specifically, the Regional Municipality of Niagara does not. (My parents live there.)

There was pressure from several quarters in Ottawa to not follow them. More traffic can be squeezed through an intersection with short ambers than one with long ambers. And, there is the red-light-running issue: at least one senior Ottawa bureaucrat considers current amber light durations to be an incitement to red-light running, that they should be shortened to below the provincial guidelines, that all-red periods should be eliminated, and that automatic cameras should be used to charge every driver entering an intersection after the light has turned red, rain or shine. (But, it's easy to avoid being hit by amber light runners - just don't blindly jump-start on your green.) Fortunately, our professional traffic engineers have prevailed - regional policy is now that traffic lights shall meet the provincial guidelines for both amber and all-red periods.

Short ambers decrease safety for many road users:

The fact is, no single duration can be suitable both for a 30-year-old male in a muscle car and an OCTranspo bus loaded with standing passengers. No single duration can be suitable both for dry pavement and for asphalt covered with water, ice or slush. The focus should be on optimal safety for all, not on outrage against a small minority; on cooling tempers, not making criminals out of safe drivers.

As it stands, drivers of heavy or handicap vehicles often have to drive more slowly than the posted speed limits so they can stop safely within current amber light durations. That leads to road rage and subsequent dangerous driving by those stuck behind them. I drive a medium-weight vehicle with elderly passengers - it's downright scary to see what many drivers are willing to do to pass me when I have to drive that slowly. That kind of driving then results in expensive demands for traffic calming to reduce accidents, especially to pedestrians.

It would significantly assist road safety if the Province of Ontario would require that its Ontario Traffic Manual apply to all traffic lights in the province as minimum times. And, the province should require that enforcement take account of local weather conditions, vehicle weight, and the safety of vehicle occupants. Too-short signal change times put all of us at unnecessary risk.

John Sankey
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