TRAFFIC FALLACIES

Fallacies from the General Public

People believe many things about traffic that are false. Here are some of them, with the reasons why they are false:

You can make the green light come quicker by occasionally letting your car creep.
FALSE! This is like pushing the button on the elevator repeatedly and thinking that this will make it come faster. Once you have been detected, there is nothing you can do. The light deals with traffic in a predetermined order, and must finish with one stream before turning to another.
You can do something that will cause the light to fail to turn green. If you creep up beyond the stop line, you are no longer in the detection zone. The signal thinks you turned right on red and forgets you entirely. Then, another car must arrive to retrigger the detector before the light can turn green.
Because left turns go first at traffic lights, they should go first at ALL-WAY-STOP intersections.
FALSE! This cuts down the traffic capacity of an ALL-WAY-STOP. It is much more efficient for a left turn to start moving just after the oncoming car starts to move, and then tuck in behind it. The traffic light puts the left turns first to avoid yellow-trap -- a dangerous condition -- and because it can more efficiently use green time that way.
Where both approaches have left turn lights that go first, and one empties out earlier, then a "smart" light can release one straight through movement earlier, since nothing blocks it.
Vehicles coming toward me are moving, but the light is still red. The drivers must be breaking the law.
FALSE! They really have a green. Signals with left turn arrows, emergency vehicle pre-emption, railroad pre-emption, or queue-discharge can release traffic from one approach while keeping the other approaches stopped. The "smart" light mentioned above does this.
The pre-emption and discharge sequences are trying to clear out traffic in one direction on purpose, to clear the way for an ambulance, a fire engine, the police, a train, or stopped traffic on a freeway.
To turn left at a traffic light, wait in the intersection until a gap appears in traffic, or until the light changes.
FALSE! In some cases, your light can turn yellow and then red without a gap appearing in the stream of traffic, leaving you frozen in the intersection. The stream may continue after your light turns red, causing the yellow-trap hazard with you in it.
Wait at the stop line until you can turn.
The yellow light is for making left turns.
FALSE! It is actually dangerous to make a left turn during the yellow at some intersections. Yellow-trap can catch you here.
Always wait at the stop line, until a gap appears in the oncoming stream, before turning.
The left lane on a multilane highway is for passing. Drivers must return to the right lane after passing.
FALSE! Such a 1920's mentality reduces the capacity of the highway by the capacity of the left lane. This is because all traffic is expected to fit in the other lanes when nobody is passing.
See my page on left-lane laws for more on this.
Some drivers love to block traffic by going slow.
FALSE! If the vehicle ahead is going slow, there is usually a SAFETY reason. If you are following too close, or have your bright lights on, that might be the reason. If so, correcting these conditions will cause the other vehicle to speed up.
Other reasons might be related to the type of vehicle ahead, such as height, width, weight, grade, center of gravity, sight distance, a load that suddenly came loose, or lack of tire traction. Also, check to see if the speed limit has changed, and if the driver might be drunk.
Widening a street to four lanes is best for handling more traffic.
FALSE! The capacity for a four-lane undivided road cannot exceed 2400 vehicles per hour in each direction. On the other hand, a pair of two-lane one-way streets can carry 3600 vehicles per hour in each direction. In either case, the capacity must be reduced by the time signals on the street are red. Also, 500 vehicles per hour must be subtracted for each line of curb parking allowed on the street.
The reason a one-way street works better is that there are no cars making left turns through gaps in traffic.
Narrowing a street to two lanes is best for handling traffic.
FALSE! The capacity for a four-lane undivided road cannot exceed 2400 vehicles per hour in each direction. On the other hand, a two-lane two-way street can carry only 1200 vehicles per hour in each direction. This is stupidity which requires finding other routes for the rest of the traffic.
This is a political solution to too much traffic in the area. It will not work if there is no place to send the other vehicles using the road.
Changing one-way streets to two-way streets improves traffic flow.
FALSE! The capacity of a two way street is a total of 1200 vehicles per hour in each direction. A two-lane one-way street can carry 3600 vehicles.
This is nothing but a political desire to remove confusion or to make trips shorter for bicycles. It does nothing to help traffic flow. The reason a one-way street works better is that there are no cars making left turns through gaps in traffic.
Higher speed limits waste more fuel than anything else does.
FALSE! Once a car gets up to speed, the only energy needed is that to overcome friction. What wastes fuel is slowing a vehicle to a stop, and then accelerating it again.
Speed limits lower than 45 mph have lower gas mileage than limits above 40 mph because most transmissions must be in a lower gear at those speeds.

Speed limits lower than 30 mph have lower gas mileage than limits above 25 mph because most transmissions must be in a lower gear at those speeds.

Traffic jams and STOP signs are the two biggest fuel wasters.
Building a new highway generates more traffic.
FALSE! Most of the traffic that "appears" when a new road is built comes from three sources:
- Trips being made anyway, which are diverted to the shorter or better route (the majority) - This results in fuel savings and lower pollution, not extra burdens.
- People who took fewer trips to a destination before because the roads were so bad.
- Customers going to new businesses that were built because of the new road.
Most people don't drive on roads just to use them. People may make one trip on a new road when it first opens just to find out where it goes and what is on it.
Stop signs are the best way to control speed in neighborhoods.
FALSE! This actually tends to increase the speed between intersections. They speed up to compensate for the unnecessary delay.
The best way to control speed in neighborhoods is to provide enough good fast roads for through traffic, so drivers aren't tempted to take shortcuts.
To make the car ahead speed up, get as close to it as you can.
FALSE! That is a good way to cause an accident. It also causes good drivers using the space-driving system to slow down.
You should always stay at least 2 seconds of travel time behind the car ahead, and adding additional seconds for higher speeds, bad weather, and slick roads.
Bicycles are pedestrians.
FALSE! Bicycles are vehicles, and are required to obey all Indiana laws governing moving traffic. The only way a bicycle can be a pedestrian under the law is if the rider dismounts and walks the bike.
See: Why bicycle lawbreaking is illegal.
Bicycles have special priority over cars.
FALSE! Bicycles are classed as vehicles, just like cars, and Indiana law requires all bicycle riders to obey all Indiana laws governing moving traffic.
Riding as though bicycles have special privileges causes most bicycle accidents.
Pedestrians always have the right-of-way.
FALSE! There are several cases where pedestrians must yield to other vehicles:
- Pedestrians are required to stop before crossing, and must wait until there are no vehicles so close that they cannot stop in time.
- Pedestrians must obey pedestrian signals.
- Pedestrians are not allowed to cross midblock at locations where traffic signals exist at both ends of the block, unless a crosswalk is installed.
- Pedestrians walking linearly along the roadway must leave the roadway when they are blocking traffic.
Pedestrians should always keep to the right.
FALSE! It depends on where they are. On sidewalks and in crosswalks, they belong on the right. But when walking on the edge of a road with no sidewalks, they should be facing the traffic, usually on the left side.
The general rule is to keep right, unless walking along a road without sidewalks.
Joggers belong on the sidewalk.
Joggers belong in the street.
Skaters belong on the sidewalk.
Skaters belong in the street.
ALL FALSE! Joggers belong on the track, and skaters belong on a rink. Neither is a legal form of transportation. Both may be on a sidewalk, as long as they revert to being pedestrians when crossing streets or when near other pedestrians.
Skates, skateboards, tricycles, toy wagons, and push cars are considered by the law to be toys, and cannot legally be ridden on the street.
Speeding is the major cause of accidents.
FALSE! Speeding is usually stressed by government, because it is easier to convict speeders and get fines (revenue for greedy government). The real causes are:
- Speed differential between vehicles -- This is usually caused by a government setting the speed limit too low for the design speed of the road. They defend the low speed limit (to keep their ticket revenue coming in) by stating excessive speed is the cause of the accidents. But they are wrong:
  1. The passing conflicts the low limit causes are the main cause of the accidents, not the speed of those going the design speed of the road.
  2. If the road is posted at a lower speed due to a single hazard, the hazard should be removed instead of posting a low limit.
  3. Twenty five mi/hr is the lowest speed limit allowed by Federal standards, except in school zones, park zones, and alleys. Anything lower must be changed.
- Improperly set speed limits -- Indiana law requires the speed limit to be raised if no hidden hazard exists and more than 15 percent of drivers are breaking the posted speed limit.
- Following too close -- This is the number one cause of rear-end and off-the-road accidents. The car following too close scares the driver in front into driving faster than is safe with two vehicles that close together. Any sudden emergency will cause a rear-end collision, or will cause the lead car to leave the road.
  The officer usually cites "excessive speed," and blames the driver who ran off the road, not the one pushing him (who is not there to be arrested).
- Alcohol and drugs -- Impaired driving causes more accidents than any other one cause.
- Using a cell phone while driving -- This causes almost as many accidents as impaired driving does. Using a telephone or a computer while driving should be prohibited.
- Bad sight distance -- This causes drivers to proceed when the way is not clear.
- Failure to yield -- Drivers in a hurry take chances, usually taking the right-of-way from other vehicles. Those vehicles might not stop in time, might evade into the path of other vehicles, can hit pedestrians, or can run off the road.
Too often, police officers cite "excessive speed" when there is no apparent cause of an accident (and especially when nobody is left alive to tell what happened). This wrongly gives speed more weight in the eyes of government than it deserves.
Traffic lights prevent accidents.
FALSE! Traffic lights prevent accidents only when they are warranted, and only when they are properly installed and operated. Any signal that causes yellow-trap, or makes it impossible for a driver to stop in time, will cause accidents.
Accidents will also be caused by drivers following too close at traffic lights.
Parallel parking is best on high traffic streets.
Angle parking is best on high traffic streets.
BOTH FALSE! Off-street parking is best for high-traffic streets. Parking at the curb subtracts 500 vehicles per hour from the lane next to it. If the parking area was a lane, the street could handle 1800 more cars an hour.
Parking lots should have one-way drives and 45-degree angle parking, with stop blocks or sidewalks between the rows to keep vehicles from exiting in the wrong direction.
Elected officials are the best people qualified to make traffic laws.
FALSE! Election to office does not impart training in traffic engineering. Trained engineers are much better equipped to make decisions involving the safety of moving traffic.
Politics should be kept entirely OUT of the process of designing the best streets and roads.

Fallacies from Politicians

Politicians believe even stranger things about traffic that are false. These are examples of the reasons why politicians should not be in charge of traffic control:

Motorists will speed, unless the police work hard to prevent speeding.
FALSE! Given a lack of hidden hazards, most drivers will drive the design speed of the road.
The problem occurs when politicians set speed limits slower than the design speed of the road. They claim that they do this to make the road "safer." But the real reason they do this is an ulterior one: More traffic fine revenue for the budget. This conflict of interest is one of the main reasons why traffic control should be taken away from politicians.
Synchronizing traffic lights works on all streets.
FALSE! Traffic lights can not be progressed on all streets (the correct term is progression, not synchronization). The following are constraints on how well progression will work:
- Progression works much better on one-way streets.
- Two-way streets are more difficult to progress.
- Progressed streets must be several blocks apart. The streets in between can't be progressed.
- Short blocks, diagonal streets, and irregular block lengths make progression much harder to achieve.
- Traffic actuation usually makes progression worse. The exception is a side street in a poor location that can skip with no traffic.
- Intersections with left turn signals in all four directions usually can not be progressed.
- Progression works better if minor side streets have stop signs, instead of traffic lights.
- Progression can be aided by prohibiting minor movements or using half signals (which stop only one direction of travel on the progressed street).
- Progression can be aided with lead-lag phasing at some intersections. But this requires either exclusively-protected left turns (left turn only on green arrow), or the Flashing Yellow Arrows left turn system.
Slowing drivers down saves energy.
FALSE! If drivers slow down of their own volition, it will save energy, as long as the slowing down doesn't require shifting to a lower gear. But if the following methods are used, the slowing down wastes energy, instead of saving it:
- Stop signs used for speed control. Stop signs waste more energy than any other road feature.
- Methods that cause drivers to repeatedly follow curves or make sharp turns.
- Speed bumps or humps. These cause drivers to vary speed, wasting energy. They also damage cars. There should be a federal penalty for using any kind of speed bump or hump.
- Mini roundabouts. They are better than stop signs, but are worse than methods that don't slow traffic at intersections.
Slow driving saves energy only when it is done at a uniform speed and direction. And it really does not save that much.
Metering traffic solves congestion problems.
FALSE! Metering doesn't prevent congestion. It just moves the congestion to the metering locations and to other roads. Nothing is a substitute for providing enough capacity for the demand.
Note that zoning often increases congestion by increasing the length of trips to and from work.
Mass transit solves congestion problems
FALSE! Mass transit doesn't solve congestion problems, for two reasons:
- Most people can't use mass transit, because they aren't on the route, don't have enough time, or need to carry freight.
- Mass transit vehicles stopping to pick up and drop off passengers block traffic, making MORE congestion (mess transit?).
The left lane on a multilane highway is for passing. Drivers must be required to return to the right lane after passing.
FALSE! Such a 1920's mentality reduces the capacity of the highway by the capacity of the left lane. This is because all traffic is expected to fit in the other lanes when nobody is passing.
See my page on left-lane laws for more on this.
Widening a street to four lanes is best for handling more traffic.
FALSE! The capacity for a four-lane undivided road cannot exceed 2400 vehicles per hour in each direction. On the other hand, a pair of two-lane one-way streets can carry 3600 vehicles per hour in each direction. In either case, the capacity must be reduced by the time signals on the street are red. Also, 500 vehicles per hour must be subtracted for each line of curb parking allowed on the street.
The reason a one-way street works better is that there are no cars making left turns through gaps in traffic.
Narrowing a street to two lanes is best for handling traffic.
FALSE! The capacity for a four-lane undivided road cannot exceed 2400 vehicles per hour in each direction. On the other hand, a two-lane two-way street can carry only 1200 vehicles per hour in each direction. This is stupidity which requires finding other routes for the rest of the traffic.
This is a political solution to too much traffic in the area. It will not work if there is no place to send the other vehicles using the road.
Changing one-way streets to two-way streets improves traffic flow.
FALSE! The capacity of a two way street is a total of 1200 vehicles per hour in each direction. A two-lane one-way street can carry 3600 vehicles.
This is nothing but a political desire to remove confusion or to make trips shorter for bicycles. It does nothing to help traffic flow. The reason a one-way street works better is that there are no cars making left turns through gaps in traffic.
Red-light cameras improve safety.
FALSE! Red-light cameras improve only the coffers of greedy local governments. In order for the cameras to pay for themselves, governments have been shortening yellow lights to catch more "violators." In addition, the cameras don't identify the driver. It is wrong to issue the ticket to the owner.
Here is another main reason politicians should not be controlling traffic. Proper design is the way to prevent red light violations:
- Provide enough yellow time. It should be a minimum 4 seconds, longer for higher speeds.
- Provide red clearance. But do not enforce red clearance. It is needed to safely stop or clear.
- If vehicles near the weight limits regularly use the road, provide longer clearance times.
- Make sure there is enough sight distance. Trees blocking the view must be removed.
- Provide enough capacity. Stopping several times at the same signal makes drivers cheat.
- Don't let the light change with vehicles in the dilemma zone (where the driver can't stop, and can't clear).
- On high speed approaches, use some form of distant signal.
- Don't favor side street traffic by setting the maximum green time too short.
- If a red-light camera must be used, don't enable it until after a conflicting signal is green.
Advance warning of the end of the green increases the hazard.
FALSE! It increases the hazard only when it is implemented wrong. The mistakes made in this area are:
- Giving too much advance warning with a countdown display. The indication must be provided within a few seconds.
- Placing the indication at the stop line. It should be placed before the dilemma zone.
- Timing it wrong. The indication should change when drivers should stop instead of trying to clear.
- For the incessant red light runner, red-light cameras are appropriate. With the distant signal warning them, innocent drivers won't be caught.
- Because drivers can't estimate distances well, marking the decision point with a marker on the side of the road might increase safety. When the detector loops are visible, some drivers use those for the decision point.
The advance warning, if given, should be in the form of a distant signal.
Overdesigning the road makes it much safer.
FALSE! Overdesigning the road makes it safer - if the speed limit is set to the actual design speed. The trouble with overdesigning occurs when the facility is designed for one speed, but signed for a lower speed. This causes a speed differential, as half the drivers obey the speed limit, while the other half of them drive at the real design speed of the road.
The speed differential is more dangerous than the safety gained by overdesigning the road, and enforcement will not be able to cure either the speeding or the speed differential.

One engineering fact that emerges in most speed investigations is that, if more than 15 percent of the drivers are speeding, then the speed limit is wrong, not the drivers. Overdesigning the road almost always causes this effect. And again, enforcement will not be able to cure it.
There is nothing wrong with passing traffic laws for non-traffic purposes.
FALSE! Passing traffic laws for non-traffic purposes causes obedience and enforcement problems. Speed limits should always be set for the design speed of the road, not the political whim of a layman politician. Stop signs and traffic signals should be installed where they are needed, not because a pressure group wants them.
Using traffic laws for other purposes dilutes the perceived necessity of such laws for safety. When people see the phony uses of traffic laws for ulterior motives, they then don't trust the necessity of other traffic laws passed to prevent real dangers.

One "traffic" law that belongs in the trash can is the law that lets government suspend driver's licenses to collect money owed to a government. Government is diluting the severity of a license suspension by using it as a substitute for a collection agency. This instead causes people to ignore license suspensions, so they drive while suspended. Governments should use real collection agencies to collect any money owed them, rather than taking away driving privileges to satisfy their greedy desires for more money. Legislators who pass such laws should be thrown out of office for violating the public trust.

Traffic fines must NEVER go into general funds for governments to spend. They should go into special funds to reimburse crime victims.
Blanket speed limits for certain classes of roads or types of jurisdiction reduce costs, with no disadvantages.
FALSE! Blanket speed limits do reduce the costs of signing. But there are several problems with such a method of administering speed limits:
- Lack of notice: Strangers can't figure out the speed limits, because there are very few signs. Special knowledge (having read newspapers in the area affected) is needed to correctly obey the law. Travelers are unlikely to have seen those newspapers. Courts are likely to throw out convictions made under such laws (unless the fines fund the judge's salary).
- Lack of flexibility: Roads designed for different speeds will be signed or enforced for the wrong speed limit, causing speed differential problems.
- Change made, but not due to a change in traffic: The speed limit is changed when a municipality annexes the road. This causes the speed differential problems, because nothing on the road actually changed. This is made worse when a city will not spend the money for the study needed to change the speed limit back to the design speed.
- Difficulty in ascertaining which speed applies: Sometimes it is hard for a driver to determine whether or not he is inside a city limit. There is usually (but not always) a sign telling when the road enters a city, but there are usually no signs telling a driver he is leaving a city. Making certain speed limits apply inside cities removes the savings, because either speed limit signs must be posted on exit from cities, or signs showing exit from a city limit must be posted.
Speed limits should be signed in such a way that any driver turning onto a road can find out the speed limit before violating it. Too often, governments don't think of any traffic other than traffic going straight on the road. This mistake is especially hazardous when a government signs a school speed limit at only the main entrances to the speed zone.

This is a good argument for the abolition of municipal governments. There is nothing necessary that a municipal government does that a county government can't also do.