Of late, there's been a spate of fatalities at the Moolchand Crossing Underpass on Delhi's Ring Road. Nothing sinister about this road except that in preparation for the upcoming Commonwealth Games, most roads are being spruced up. This particular underpass is being given the 'mastic Tarmac' treatment wherein 2 inch thick tiles of rubberised tar tiles are glued to the existing tarmac surface. The problem lies in the fact that this work is done in stages and it creates a two-inch thick height difference, with a sharp demarcation edge, between the old and the new surface till the time the entire road is uniformly covered. I had happened to pass through the underpass late last week and saw that the road was being thus treated in longitudinal sections and almost one-third width of the road was covered with the mastic tiles while the rest was old tarmac.

See the article below for details of the process and the present situation at the underpass.


HindustanTimes ePaper - Article

The point of concern for us at xBhp is obvious. These are two-wheeler riders dying there. And it is important for us to discuss and assess the possible reasons behind these fatalities. Hereon, I'll put forth my contention and initiate a discussion on the issue so that we all end up with a thorough understanding of the situation.

My take is that the difference in height between the adjacent surfaces is the real death-trap for the two-wheelers. The height difference causes the vehicle to tramline, the rider looses control and either falls and gets run over by a bigger vehicle behind him or hits the vehicle he's adjacent to. There can be another reason which has to do with the sudden increase in road height at the point where the re-carpeting work begins. this sharp crest could well unbalance a two wheeler, especially those with small diameter wheels like scooter. And almost half of the accidents in this case have involved scooters.

The figures below show how the larger diameter wheels of a motorcycle are at a big advantage here.







But tramlining appears to be a bigger villain here and so lets discuss it at greater length.

Tramlining happens when directional control of a vehicle is disrupted by its tendency to follow the longitudinal ruts and/or grooves in the road. It's name could be compared to the tram or trolley driver who does not steer because his vehicle follows the path established by the tracks. Tramlining is the result of a tyre's grip on the road and any vehicle running on rubber will experience tramlining. The tyre grips the road due to friction and any rut or groove tends to 'catch' the rubber at the contact patch and tries to 'carry' it along its path. 4 wheelers show a tendency to pull sideways when a tyre tramlines. But for two-wheelers this becomes critical as the tyre can catch the groove so hard and so suddenly that the resulting force can snatch the handlebars out of the rider's grip. One can well understand the result when the bike suddenly tracks along the rut or groove without any restraining control of the rider. The resulting fall can turn out to be just the beginning of more serious consequences on a road as busy as this underpass.

I'll try and put forth a visual picture of the situation and propose certain established maneuvers that can help a rider avoid such a situation fro getting out of control.

The figure below depicts the asymmetric contact patch that the tyre has as a result of the height difference between two surfaces of the road.


One of the best and foremost ways of avoiding letting your bike's tyre get caught like this is to avoid riding anywhere close to the edge. Ride either on the lower level or the higher level but don't try to change lanes across the height difference. if a vehicle brakes in front of you, slow down with it rather than cutting across the groove at the same speed.

There is an established method of handling such situations. I'll begin with a situation where there's a defined rut or groove in the riders path, at an angle to his direction of travel and deep enough to catch his front wheel hard enough to wrench the handlebar out of his grip.



The trick here is to cross the rut as perpendicular to it as you can. Steer you bike (of course check those RVM's for vehicles behind you before going for this 'S' move) such that you cross the rut at right angles to it. Any more or less than this 90 deg angle increases the chances of the rut catching your wheel.

For a situation where the 'rut' runs parallel to your direction of travel as is the case at the Moolchand Underpass, there's a milder version of the same maneuver. But this needs to be done at a far slower speed than you can be in the case discussed above. see the picture below for the right and wrong ways of handling crossing over a longitudinal rut.

The wrong way first. Don't try top sneak across the road imperfection.



Instead, be decisive (which you can only be if you're sure there's no one behind you close enough to hit you or run over you), slow down and cut across the rut at as close an angle to 90 deg as you can. This again is a smooth 'S' move. The need to slow down is important as no matter how much you turn, you will not be able to hit the rut at anywhere close to perpendicular. There will be some amount of 'tramlining' tendency by the tyres. The point is to keep this force generated by tramlining as low as possible and the only way you can do this is by going real slow.



The better the tyre grips the road, the harder will it tramline. Wide tyres tramline more than narrow ones, primarily due to the fact that there's less rubber to hang on to the rut. Also, the tramlining tendency is greatly increased when there's a large difference between the relative width of the front and the rear tyres. people who 'love' that w i d e rear will also be the first one's to get thrown off their bikes when they hit such a rut. In their case, the front will get forced out by the rear tyre, which will in turn get stuck in the rut. Since the front is way narrower than the rear in such a case, it cannot generate enough grip to pull the rear out of the rut. the result is a momentary wiggle, an oscillation of the front and a fall which is a copybook demonstration of undamped harmonic oscillation.

I am reproducing this same article in the 'Ride Safe with me' section. However the discussion can continue here in this thread.