Well,I may be way off..but I thought of ths ridiculous thing..

If traffic moves on the right,on both sides,it will be close to the median of the road.So,all the weight which was till now along the sides is now concentrated at the centre.

This is the ridiculous part- with so much weight shifted to the centre of the road, there will be a slight depression there...so the net radius of the earth would,I guess decrease..so it will rotate faster..coz centripetal force is inversely proportional to radius.Hence,the day would be shorter.