By John S. Allen, CRW Safety Coordinator
Safe and cooperative operation of a bicycle—or any vehicle—requires cooperation with other road users, making it possible for many vehicles at once to travel in reasonable safety, faster than walking speed. The traffic law is often the first and only thing people think of in this context—but the traffic law only codifies the rules of the road, and the rules of the road rest on the foundation of the more basic rules of movement, which are based on logic, the characteristics of vehicles, and human abilities
Human abilities
Safe and cooperative operation of a bicycle—or any vehicle—requires cooperation with other road users, making it possible for many vehicles at once to travel in reasonable safety, faster than walking speed. The traffic law is often the first and only thing people think of in this context—but the traffic law only codifies the rules of the road, and the rules of the road rest on the foundation of the more basic rules of movement, which are based on logic, the characteristics of vehicles, and human abilities
We humans are social beings who can cooperate with one another. We have a fine ability to judge time and spatial relationships, but we have a perception and reaction time and eyes only in the front of our heads—looking forward is easier and more convenient than looking to the rear.
Characteristics of vehicles
Vehicles move most easily in a straight line and have physical limitations on how sharply they can turn and on stopping distance. This leads to our first rule of movement:
First come, first served
The bumper sticker saying “I may be slow, but I'm ahead of you” puts it rather well. And in this context:
Safe following distance
Drivers must look ahead of themselves most of the time, to steer their course. The speed capabilities of vehicles differ greatly. A vehicle ahead may have to slow or stop suddenly to avoid a hazard. Vehicles can brake much more abruptly than they can accelerate.
For all of these reasons, the driver of a following vehicle is held responsible for avoiding a collision with a leading one. Imagine the opposite: that the leading driver would be required to accelerate and increase the risks ahead to avoid one behind, if acceleration is even possible. No thanks! Overtaking is allowed only where safe. This also reflects the human abilities and limitations described earlier.
Driving on the right
To avoid colliding with traffic from the opposite direction, drivers keep right—or left, in some countries. This is the only rule of movement which is completely arbitrary. It can work either way, as long as everyone follows the same rule.
For the remainder of this discussion, we will assume that vehicles keep right.
Speed positioning
On a two-way roadway, stopped traffic is at the edge, slow traffic closer to the center, and overtaking traffic may cross the centerline. On a one-way roadway, or one with more than one lane in a given direction, overtaking on either side may be permitted, but overtaking on the right is generally restricted in order to keep speeds more consistently slower at the right edge.
Because attention is focused mostly ahead, the driver of the overtaking vehicle must take the initiative, must evaluate the situation and determine when it is safe. The driver who is being overtaken must not prevent safe overtaking by speeding up. If overtaking is not possible for a long time, the leading driver must pull aside when a safe opportunity arises.
Priority to through routes
Now we begin to address traffic that moves in different directions.
For the sake of efficient traffic flow, a vehicle entering a roadway from a private driveway or parking spot must yield to traffic already on the roadway. Traffic on a minor road yields to traffic on a major road, as usually indicated with a stop sign or yield sign. Some other countries, notably France, use the priority for the vehicle on the right more broadly, even when it requires yielding to a vehicle on a minor road
Changing lane position
Changing lane position may be necessary to change to overtake a slower vehicle, to prepare to turn, or because the usable roadway narrows—for example, when there is a double-parked car ahead.
In all of these cases, a merge to the new lane position is carried out in advance of the need to be in the new lane, when it is safe to look to the rear for overtaking traffic, and as traffic permits –when another vehicle behind is not approaching in the new lane or lane position.
Turns are prepared with a merge to the right before turning right, and to the center (or the left side of a one-way roadway) before turning left. Once having reached the correct lane position for a turn, the driver can focus attention on traffic to the front, in the intersection, avoiding the need to look both backward and forward at the same time.
Understanding lane positioning is especially important for the operator of a bicycle or motorcycle, who needs to choose not only a lane, but also a position within a lane.
Intersection yielding rules
The fundamental rule for intersections is that turning vehicles yield to through traffic. Right-turning vehicles yield to traffic coming from the left. Left-turning vehicles yield to all other traffic, because they are not only turning, but also cutting across the path of through traffic.
When two vehicles arrive at an uncontrolled intersection at right angles at approximately the same time, the one on the left is required to wait, as it has an extra half road-width in which to stop.
In rotary intersections, all traffic in the circular roadway comes from the left, and that rule for uncontrolled intersections applies. That s how rotaries can work without traffic signals.
A T intersection, a yield sign or stop sign is at least in theory not needed, as traffic entering from the “vertical” leg of the T can only turn right or left.
Signaling
A turn signal may be a courtesy, a warning, or a request. Signaling a left turn informs another driver that it is unsafe to overtake on the left. Signaling a right turn informs a driver in the cross street to the right that it is OK to proceed. When a driver is intending to change lane position, a turn signal is a request to another driver to extend courtesy and make room.
Brake lights or a slow signal made with the hand provide a warning that a vehicle is slow or stopping, Especially for bicyclists and other operators of slow vehicles, a slow signal may indicate that it is unsafe to overtake.
Many signaling laws date back to before 1950 when motor vehicles did not yet have electrical turn signals, and all hand signals had to be made with the left hand extended out the driver’s window. Many jurisdictions now allow bicyclists to make a right-turn signal with the right hand. This makes a lot more sense, because the hand points point to where the cyclist is going. Massachusetts also allows the slow signal with the right, and that can work better too if the bicyclist is to the left.
Traffic controls
Signs, signals and markings may be needed to refine or even overturn the default rules when a street is wide, traffic is heavy or fast, or sight lines are short. A yield sign or “tiger tooth” pavement markings indicate that cross traffic has priority. A stop sign or flashing red light requires a yield, but also a stop, sometimes necessary for safety. Other signs indicate special rules such as speed limits, or warn of hazards.
Traffic signals establish different times for different traffic movements. Lane markings may establish zones where overtaking is or is not permitted; designate lanes for different destinations; or restrict use to particular types of vehicles, but in the latter case should never overturn the obligation to merge to the lane appropriate for the destination.
Yielding to pedestrians
Generally, drivers must yield to pedestrians in crosswalks, though traffic signals may establish a different priority. Drivers may or may not be required to yield between crosswalks, depending on applicable laws, and especially not close to a crosswalk.
Summary
To sum up: vehicle operation can be described as a form of continually mutually-improvised group choreography based on the rules of movement, which reflect human abilities and characteristics of vehicles to optimize safety and efficiency of travel. The traffic law rests on that foundation, codifying the rules, setting qualifications for operation of vehicles, establishing penalties for violations, and determining fault in the case of a mishap.
A Caveat
The traffic law does not teach skills needed for safe operation. Skills must be learned elsewhere, through instruction, practice and experience.
