JOHN S. ALLEN'S BICYCLE FACILITIES, LAWS AND PROGRAMS PAGES
A LOOK INTO THE "BIKE BOX"
This article addresses technical issues with bike boxes. I have also published an article further addressing the in-line bike box (see definition below) and an article discussing political rationales.
What is a "bike box"
There are two common types of "bike box."
(Note: the descriptions that follow assume that traffic normally keeps to the right side of the road. For consistency in the examination of delays due to traffic signals, intersections are assumed to have two streets that cross one another, and a bidirectional green phase of equal length for each. Any increase in the number of streets and signal phases e.g., separate left-turn phases, will increase delays relative to the total signal cycle time.)
The cross-street bike box
One kind of bike box, shown in the photo below, facilitates a "two-point left turn" or "box turn". This type of turn is commonly used by child and novice bicyclists, or at intersections where vehicular left turns are prohibited. In this type of left turn, bicyclists -- and sometimes motor scooter riders, as in the photo below (more details about this location) -- proceed to the far right corner of the intersection, turn left in the cross street, and proceed when the traffic clears or the signal changes.
I'll call this type of bike box the "cross-street bike box."
Designated waiting location for two-point turns (An Ho Road
Harbor Road, Taichung, Taiwan).
The following considerations apply to the cross-street bike box:
The in-line bike box
The other kind of bike box is implemented in connection with an advanced stop line and is located before the crosswalk -- as in the photo below of an installation in Germany. I'll call this type of bike box an "in-line bike box".
public domain -- from a
Cross-street bike box
At a signalized intersection, the cross-street bike box involves an average wait of 3/4 signal cycle when the bicyclist arrives on the red or 1/4 when the bicyclist arrives on the green, for an average delay of 1/2 signal cycle. With or without signals, there may be time waiting in queue to enter the intersection and time waiting in the bike box for traffic to clear.
The distance traveled when using the bike box is longer than for a vehicular left turn, and so bicyclists' travel time is longer unless the bicyclist can overtake a long queue. This is more rarely the case at an unsignalized intersection, but the wait is shorter if the cross street has priority (for example, if there is stop sign for the street from which the bicyclist initially approaches the intersection).
In-line bike box
An in-line bike box can reduce delays for bicyclists who operate lawfully only when motor traffic is congested and backs up at traffic signals, and when the bicyclists can overtake stopped motor traffic. The average delay for bicyclists who arrive on the red is 1/4 signal cycle, plus whatever time is required for left-turning bicyclists to yield to oncoming traffic.
When the light is green and motorists are passing through the bike box, bicyclists traveling straight ahead or turning right may proceed as usual. But left-turning bicyclists must wait on the green light and then proceed into the bike box on the red. Here's an observation of a bike box in London, England by Alan Forkosh:
[T]he use of left and right are reversed from American practice in the following description.
(We now return to drive-on-right North America.)
Bicyclists who wait on the green light to turn left stand in the way of other bicyclists who could go straight through or turn right without waiting, and who otherwise would experience no delay. The average delay for all of these cyclists, then, is 3/4 signal cycle, plus whatever time is needed to yield to oncoming traffic, and the average wait for left turns made by swerving into the bike box is 1/2 signal cycle waiting for the signal, plus the time waiting for traffic.
Because of this problem with congestion,, bike boxes are not recommended as an implementation for left turns in England, according to John Franklin, author of the book Cyclecraft.
Another option for a left turn when arriving at the bike box on a green is to continue straight ahead and make a two-point turn, as Alan Forkosh described, involving an average delay of 1/2 signal cycle. Other bicyclists waiting to enter the bike box and turn left from it may, however, block progress toward the far right corner and increase the delay.
Sometimes a bike lane is provided between travel lanes rather than to their right, as shown in the photo below from Vancouver, British Columbia.
In the installation shown, bicyclists must merge across a lane of traffic to reach the approach bike lane -- but then are directed to swerve either to the right or to the left in front of waiting motor traffic once they reach the bike box. Peter Stary comments:
Mr. Stary is describing the bike box as a way to accommodate bicyclists' disorderly behavior by meeting it halfway. Elsewhere in his comments, he mentions an advance warning for the bicyclists as a possibility. Lacking one, the installation requires motorists to yield to bicyclists approaching from behind while also paying attention to traffic ahead of them.
I would submit that the issues of filtering forward and of swerving into the bike box are separate. There is a correct lane position to approach the intersection for each of the four destinations shown -- but here, or anywhere, no single bike lane can lead a bicyclist to the correct lane position for more than two destinations. In this installation, a bicyclist could proceed from the bike lane to either of the two destinations that are nearly straight ahead (keeping to the right side of the overpass, or the left side of the one-way street which is to its right), without crossing the path of other traffic. A left or right turn would require the bicyclist's merging to the middle of the appropriate lane before reaching the front of the queue.
It comes down to this: lacking separate signal phases, bicyclists' understanding and accepting merges into lines of motor traffic is a necessary element of any solution which does not lead to conflicting movements. And separate signal phases have their own problem: increased delay and resulting increased temptation to disobey the signal.
Merging, and the vehicular left turn
Now, let's look at left turns in the absence of either type of bike box.
A bicyclist who signals and merges left before reaching the intersection, like other drivers, can almost always get the cooperation of an overtaking motorist. The bicyclist then can execute a vehicular left-turn. The vehicular left turn maneuver is explained on another page on this site. Or the bicyclist may merge only far enough to deter a "right hook" (motor vehicle turning right from the bicyclist's left side), and then execute a two-point turn.
These maneuvers allow a bicyclist to approach the intersection at any time, as long as traffic is flowing freely. The delay for a two-point turn is as with a cross-street bike box. The typical delay for a vehicular left turn is much shorter than for either type of bike box, except under congested traffic conditions. In an ordinary 4-leg signalized intersection without special left-turn signal phases, a vehicular left turn at a signalized intersection involves an average wait of 1/4 signal cycle when the bicyclist arrives on the red, or none when the bicyclist arrives on the green. Thus, the delay averages 1/8 signal cycle.
Motorists waiting behind the left-turning bicyclist are less likely to have to wait than with the in-line bike box, because the bicyclist may arrive at the intersection after the start of the green phase, rather than always starting just when the light turns green and opposite-direction traffic is heaviest. In a lane that carries both left-turning and through traffic, the through-traveling motorists may often overtake the bicyclist on the right, but the bicyclist may have to control the lane (wait in the center of the lane) to avoid motorists' overtaking on the right to turn left.
When preparing a vehicular left turn, a bicyclist may still move forward if there is an open lane to the right of a queue waiting to turn left. If all lanes are backed, up, filtering forward is more difficult, and is illegal in many jurisdictions. Even if there is a bike lane, the bicyclist must cut across through stopped traffic to reach the left-turn position, taking caution to have been seen by the next driver in each line of traffic. In either case, the bicyclist is safest to wait behind the first stopped vehicle, which could start up without warning when the light changes.
In the Vancouver example, similar considerations apply to right turns when a bicyclist approaches the intersection in the bike lane. As motorists right turns on red are prohibited, the delay for bicyclists waiting in line is the same as for those who turn left. The delay once reaching the head of the queue is likely shorter because there is no need to yield to traffic coming from the opposite direction.
Cross-street bike box
Safety considerations with the cross-street bike box occur:
A cross-street bike box raises safety issues for motorists in addition to those for conventional vehicular maneuvers. In particular, motorists in the cross street must wait farther back from the intersection, compromising their ability to scan for traffic before entering the intersection. Motorists may have to slow or stop again in the crosswalk or bike box to scan or yield right of way.
As the cross-street bike box is between the crosswalk and the intersection, it raises no issue of conflicts between bicyclists and pedestrians. Quite the contrary, bicyclists who might otherwise wait in the crosswalk to make a two-point turn now have a dedicated space in which to wait.
All in all, the safety issues for a cross-street bike box are relatively minor, as long as it is placed out of conflict with right-turning traffic. The bicyclist follows a course that is mostly in plain view of other road users, and only moderately different from conventional and common bicycle and pedestrian movements.
In-line bike box
The illustration below shows some safety issues inherent in an in-line bike box.
A collision between a swerving bicyclist and a motorist starting up on a new green is most likely when there is no other bicyclist already in the bike box. The image below illustrates this issue.
Bicyclist (b) had the bad fortune to enter the bike box just as the light changed. Motorists coming from her left have little time and distance in which to avoid her. She is in the same quandary as a bicyclist crossing against the light on the left sidewalk. except that as she comes from behind, motorists waiting at the light have a smaller likelihood of having seen her.
So, she is at risk of being struck by the truck as it accelerates. Its driver has not seen her over its high hood. She also is at risk of being struck by the car that is overtaking the truck. The truck hides her from the car's driver.
Bicyclist (a) is at risk of going under the truck's rear wheels if it turns right.
At (c), however, a bicyclist entering the bike box is safer because motorists will be waiting for the other bicyclists who already are in the bike box. And the bicyclists in the bike box are visible to motorists who might turn left in front of them, unlike bicyclists who start out from a bike lane to the right of a motorist who is waiting to turn left.
Because it is never safe for a bicyclist to swerve out in front of a motor vehicle that might start moving, an in-line box installation creates an inherent conflict in yielding rules under any of the following conditions.
Lacking a special warning, the bicyclist might be able to use incidental information to figure out when the light is going to change to green. The bicyclist might, for example, notice that traffic in the cross street is coming to a stop -- however, there might be no traffic in the cross street. Or a pedestrian signal may provide a clue -- but timing and actuation of pedestrian signals vary, so this approach is not reliable.
All in all, lacking a special warning signal, a bicyclist can not be sure that it is safe to enter an in-line bike box unless he or she has recently seen the light turn red.
On a green light, a swerve into the bike box is like any other swerve left from the right curb in a lane of moving traffic. It can not be made safely without yielding to overtaking traffic. But the look back at this point also is hazardous. A bicyclist, like any driver about to enter the intersection, needs to be looking ahead for traffic in the intersection. It is preferable to merge into the flow of motor traffic well before the intersection and make a vehicular left turn or two-point turn.
An in-line bike box becomes increasingly impractical on wider streets, because the bicyclist must cross more lanes of traffic to reach the left turn position, and the required warning time becomes longer. A British Web site suggests that a bike box is questionable when the bicyclist must cross into the second travel lane, and undesirable with more lanes. An in-line bike box is therefore not practical at intersections where left turns are most difficult. Even with only two lanes approaching the bike box, a vehicle in the first lane can totally conceal a bicyclist and a motorist in the second lane from one another, as shown in the illustration above.
Some jurisdictions have mandatory bike-lane laws, and depending on their wording, the bicyclist may not have the lawful option to make a vehicular left turn. The two-point turn, however, is legal almost everywhere if conducted with a stop and change of direction, and is a favored option for child and novice bicyclists. It delays the bicyclist no more than the left turn using the bike box, though more than a vehicular left turn unless traffic is backed up. Experienced bicyclists use the two-point turn only at the few locations where the vehicular left turn is unlawful or impractical.
The traffic rules that follow are excerpted from the Uniform Vehicle Code, which is the basis for the traffic law of most US states.
Throughout the USA, a bicyclist is defined generally as having the rights and duties of a vehicle operator. Vehicle operators including bicyclists may overtake on the right under certain specified conditions.
This rule generally permits bicyclists to overtake cautiously on the right to approach a bike box.
Bicyclists generally may turn left as vehicle operators, or with a two-point turn from the far right corner of the intersection -- or they may leave the road entirely and use crosswalks. One or more of these options may be prohibited by application of the following rule:
Under this rule, authorities may require bicyclists to make left turns in special, nonstandard ways including use of the bike box. Many bicycling advocates dislike this rule, because it can be used to prohibit the generally-faster vehicular left turn, and to make nonstandard and hazardous maneuvers mandatory at the whim of a jurisdiction with little understanding of bicycling. However, this rule applies only to left-turning bicyclists and not to bicyclists who are continuing straight through.
It is not illegal to merge out from the curb -- after all, this maneuver is necessary for any vehicle operator exiting a parking space. However, drivers must use caution:
A motorist preparing to enter traffic from a parking space can wait until there is no conflicting traffic. A bicyclist entering an in-line bike box must swerve directly in front of vehicles which could start up when the light changes -- and so the requirement that a turning movement be made only in reasonable safety can not be met without an active warning traffic signal. Consider: who is to be held at fault for a collision resulting from the lack of a warning: the motorist, the bicyclist or the jurisdiction?
And how is a bicyclist to signal the intention to swerve into the bike box when hidden at the right rear of the vehicle whose driver must be notified?
The cross-street bike box may be a valid option when it avoids the need to merge across multiple lanes of traffic and wait in a long queue. A cross-street bike box is relatively free of problems and conflicts, and does not require signalization, though there is rarely justification for a cross-street bike box in an intersection which does not warrant signalization.
Where there is very heavy traffic bicycle and motor traffic going straight through, an in-line bike box may sometimes decrease delays for bicyclists, at the expense of increased delays for motorists. An in-line bike box is much more problematic when it is used for left turns or to cross to the far side of a one-way street, because in these cases, the bicyclist must wait on the green light to enter the bike box and then must wait on the red. The problems of a bike box increase with its width, and so a bike box is not useful for left turns on the multi-lane arterials where left turns are most challenging.
The in-line bike box is acceptable only at an intersection with traffic signals, and only ever decreases bicyclists' travel time if they can overtake queued traffic. This overtaking is generally facilitated by a bike lane to the right of the other lanes. Overtaking on the right, however, poses risks of collisions where vehicles can cross or turn to enter or exit streets or driveways, or if pedestrians jaywalk through the stopped traffic, or if the bicyclist is within range of opening car doors on either the right or the left...the list goes on. Generally, it is only safe to overtake slowly on the right, and often it is not safe at all.
Either type of bike box can make a left turn easier and faster only when traffic is heavy, and even then, the bike box often involves more delay than a vehicular left turn. Use of a bike box should therefore never be mandatory. Bicyclists should be permitted to cross intersections according to normal vehicular or pedestrian rules.
A "right hook" collision can occur between a bicyclist and a right-turning vehicle with either type of bike box. But with the in-line bike box, a bicyclist who turns left in front of a motor vehicle just as the traffic light turns green runs an additional risk. This risk is very serious with a large vehicle whose driver can not see a bicyclist next to the vehicle's right front corner, or if the bicyclist continues to the next lane, where a vehicle is approaching. Though a bicyclist might be held at fault for turning out across the street when it is not safe, the jurisdiction also might be held at fault for encouraging this action, particularly if the bicyclist is a child and a higher standard of care applies. The hazard can only be properly addressed by providing an active warning signal.
A critique of an installation may be found at: "Bike box" at Garden Street and Concord Avenue, Cambridge, Massachusetts.
An illustration of a four-interval traffic signal and a list of countries in which it is used may be found at http://en.wikipedia.org/wiki/Traffic_light
www.camcycle.org.uk/campaigning/papers/AdvancedStopLines.pdf -- page 4 of the PDF shows a dual-signal installation. However, cyclists are passing the first signal on the red. It is unclear whether the timing of the two signals is different so as to give bicyclists a warning, or whether the cyclists are proceeding lawfully. Page 7 shows a separate bicycle signal, but used to give bicyclists a head start. This document gives a survey of bike box installations in Cambridge, England, and favors them, though it advocates a large enough number of improvements to cast doubt on its positive evaluation.
http://www.westminstercyclists.org.uk/index.htm?asl.htm The data reviewed here indicate that motorist encroachment into the bike box is a major concern.
Study of Eugene, Oregon bike box used to facilitate crossing to ride on the opposite side of a one-way street. Note, this is the version submitted to the Federal Highway Adminstration. A revised version appeared in the Transportation Research Record. One revision was the removal of the photo on p. 14 of the report (p. 21 of the PDF document) showing what is described as a conflict between a bicyclist and a motor vehicle. It is not clear from the still photo whether the motorist had to brake or change direction suddenly to avoid the bicyclist -- who also clearly is looking back to check while merging. The video from which the photo was extracted would probably answer the question.