# Lecture – 13 Intersection Sight Distance – II

was seven point five to eleven point five In this case it is eight seconds to twelve seconds again depending on design vehicles and this range is for two lane highway with no median and minor road grade three percent or less So here half a second more value is assumed as compared to what was taken for stop controlled intersection. There it was 7.5 seconds to 11.5 seconds. In this case it is 0.8 seconds to 12 seconds Now let us try to understand the basis for this increment in time by half second. Why it is increased? It is found that minor road vehicle needs 3.5 seconds additional time to travel from decision point to the intersection for yield control approach This component was not necessary for stop controlled intersection. So this is the additional component which is required for yield control approach Now at the same time the acceleration time after entering the major road is three second less for a yield sign rather than or as compared to that for a stop sign So here it is 3.5 seconds less. Now why it is less? Because for yield controlled intersections it is assumed that drivers will reduce speed substantially but they will not stop. At least for the design consideration vehicles are assumed to travel at a slow speed but vehicles are not stopped whereas for stop control approach vehicles are required to stop. Therefore the acceleration time will definitely be higher for stop control approach because vehicles will start from zero speed, in this case it is not zero speed so there is easy saving of three seconds So there was additional time requirements of 3.5 seconds and there is a saving of 3.5 seconds So as a net result it is half a second more time that is required for yield control intersection That is why the time gap is taken as eight seconds to twelve seconds depending on the design vehicle For left turns on two-way highway with more than two lanes 0.5 seconds should be added if the design vehicle is passenger car and for each additional length from the left in excess of one that is to be crossed by the turning vehicle So I have mentioned it that the values which were mentioned earlier 0.8 seconds to twelve seconds they are for two lane highway. So if a more wider highway is considered for left turns then corrections should be applied depending on design vehicle and the number of lanes that is to be crossed in excess of one by the turning vehicle So that value is 0.5 second for passenger car and a different value is suggested for other design vehicles For right turns of course no such adjustment is necessary Departure sight triangles like those provided for stop-controlled approaches should also be provided for yield-controlled approaches This is because of the fact that if there is a conflicting vehicle then vehicles approaching