Chapter 131 Question 119

Why does humility sometimes lead to reduced efficiency on a one-way bridge? (Mario Kaporich, Scott Magrath) In Ithaca, New York, there are several bridges with one-way traffic.For years, the social norm of first come, first served governed the order in which vehicles crossed the bridge.Under this code, you should never drive onto a bridge if there is a car waiting in the opposite direction.The ostensible purpose of this specification is to prevent one-way traffic from waiting too long to cross the bridge.As mentioned earlier, social norms that encourage self-restraint lead to more productive outcomes in most cases.But in this example, humility often leads to reduced efficiency.Why do drivers have to abide by this norm?

Let’s imagine what the traffic flow across the bridge would look like if there were no regulations at all.Suppose the first driver coming from the north, finds no cars on the bridge, and begins to cross.After a while, the second driver came from the south and saw a car coming from the opposite direction, so he decided to wait until the other party had crossed the bridge before leaving.Because if the later car also drives on the bridge, the two cars will be blocked face to face on the bridge, and unless one side retreats under the bridge, no one will be able to go. Suppose it takes the first driver thirty seconds to drive across the bridge. He had just driven ten seconds before a third driver, coming from the north, drove onto the bridge.At this time, the best course of action for the second driver is still to continue to wait.If the time interval between cars coming from the north is less than 30 seconds, and each car gets on the bridge in turn, the second driver who arrives first still has to wait.When the traffic volume is relatively heavy, vehicles coming from the south may have to wait for several hours to cross the bridge.

Ithaca's social norms try to eliminate this possibility by requiring traffic in both directions to cross the bridge in first-come, first-come order.So, in the preceding case, the code requires the third driver to wait for the second driver to finish crossing the bridge before getting on the bridge.This requires self-discipline, because if the third driver starts to cross the bridge directly behind the first car, there is nothing the second driver can do.He had to wait until the third driver (and the other vehicles behind him) had crossed the bridge. What is the effect of this specification?When there is a lot of traffic in the north-south direction, the waiting time is actually longer than when there is no such regulation.

Assume that there is a tourist team of ten vehicles in each direction, and the driving interval of each vehicle in the team is ten seconds, and the leading vehicle of the northbound team arrives at the bridge before the southbound team.If the first-come-first-served rule is not followed, all northbound vehicles cross the bridge at one go, and then it is the turn of the southbound convoy to cross.Northbound vehicles do not have to wait at all, while southbound convoys have to wait a total of 12 minutes and 30 seconds. Readers only need to take a pen, a piece of paper, and do some calculations to figure it out.

Conversely, if the first-come-first-served rule is followed, after the first northbound vehicle crosses the bridge, it will be the turn of the first vehicle in the southbound convoy, followed by the second vehicle in the northbound convoy, and then the southbound vehicle. The second car of the team, so repeated.If you are patient, you might as well add up the corresponding waiting time and calculate, you will find that the total waiting time is as long as 80 minutes, and the northbound convoy has to wait for 37 in total.Five minutes later, South Xiangmu team had to wait for 42.Five minutes, six times longer than it would be without the norm.

The first-come, first-served norm not only greatly prolongs the total waiting time, but also makes the waiting time more unevenly distributed.But these problems only become apparent during times of heavy traffic, which is relatively rare for ISAB trucks. Despite this flaw, the first-come, first-served norm has stood the test of time.After each car has successfully crossed the bridge, the driver will usually pay tribute to the driver of the leading car in the opposite direction, thanking the other party for complying with the regulations and not crossing the bridge ahead of the car immediately ahead.

People sometimes make decisions based on wrong information, and other times they draw wrong conclusions from right information. Behavioral economics tells us that if we want to understand the choices people actually make in economic activities, we must analyze human motivation in more detail. In theory, cash prizes outperform other prizes of the same price.But people tend to prefer other forms of rewards. To a large extent, the choices people make stem from a psychological motivation to build and maintain personal or group identity. The first-come, first-served norm can sometimes have unwelcome consequences.