Probability that the chicken survives...

The chicken wants to cross the road on which cars circulate (all cars run at the same constant speed - 30km/h and occupy the entire width of the road). The chicken follows the trajectory that leaves him the best chance of survival. It runs at a speed of 9 km/h. The road is two meters wide. What distance will the chicken run to cross ? Write your answer in millimeters rounded to the nearest unit

Saw this question at http://treasurehunt.cijm.org/2010/