The science of no left turns

No, this is not a scientific treatise on what technically happens when one makes a left-turn while driving. I just lifted a Facebook thread title made by Ramon Sevilla in an FB group created "to discuss freely the urban development issues in Cebu." It was about turning left into USC Talamban campus, Banilad-Talamban Road. And it dwelled on the propensity of "some" citizens to break traffic laws whenever they can and get away with it.

Let's try to analyze a bit further, the advantages (and disadvantages) of No-Left-Turns, and other similar traffic management tools. We often say in our field of work, there is no right or wrong notion - everything depends on the particular situation, or in this case, intersection. It's the same as this writer's stand on flyovers - it depends on which particular intersection. Planners cannot be dogmatic and rule that all flyovers are bad and come from the devil itself. Grade separation remains as one of the better acceptable solutions in some intersections

In a two-lane road, one-lane each direction, where there's no traffic signals, it's simple. A left-turning vehicle waits until it's possible to do so without hitting vehicles from the other directions, (unless you're contemplating suicide, or you don't like the person in the other car). This creates a line of cars after you - those who also want to go left, and those who want to drive straight through the intersection. This adds up to the traffic congestion. If the road is 4 lanes (2 each direction), it's easier - the traffic is segregated to left-turning and thru-traffic. Of course, there might be weaving when some mistakenly line up in the wrong lane.

In roads with 4 or more lanes, traffic signalization is essential, since there are 12 movements (right, straight, and left x 4 directions). We need to keep in mind that signalization always introduces lags of idling/waiting vehicles. And since motorists think that movement saves time, the general perception is that flowing traffic is always better. That's why in many parts of the world, no-left-turns are often coupled with encouraging right-turns. That is, instead of making a left-turn, why not make 3 right turns and you will end up in the direction you wanted to go in the first place. United Parcel Service (UPS) actually requires its drivers to do this, saying it saves on fuel. But take note that this only works in grid city blocks.

The other option is the infamous U-turn slot of Metro Manila - you go straight, make a U-turn 600 meters further the road, come back where you came from and turn right, similar to the "Michigan Left" in the US. Another way makes the same results - turn right, then make a U-turn ahead. Then there's the superstreet, or J-turn, intersections - preventing left-turning from side streets to main streets but forces vehicles to turn right and make a U-turn ahead, instead. In all these options, you eliminate the left-turning movements.

But we already wrote in this column that these are only advantageous when the traffic volume is light. At peak hours, they actually add to the heavy congestion. The other crucial requirement for these No-Left-Turn alternatives is that you must have enough space for additional lanes before the U-turn slots, or else, the congestion stays, or may even get worse. We have to get rid of the ephemeral notion that moving traffic means better traffic, because that's not always the case.

Ultimately, the goal is to minimize travel time and the use of road space for each trip. Traffic-enhancing regulation and procedures are good, if and only if, you have the required geometric improvements, and, most importantly, you have enough space to do them. At the end of the day, this requires a level of scientific calculation to determine what the optimum solution(s) is (are). That's where the science comes in. Not through voodoo or crystal balls as what Ramon Sevilla may be forced to conclude.