A gradient of + 0.08% is followed by a gradient of – 0.07%. If the permissible rate of change of grade is 0.003 per 30 meters, the length of the transition curve, is A. 150 m B. 140 m C. 160 m D. 175 m

The correct answer is A. 150 m.

The permissible rate of change of grade is 0.003 per 30 meters. This means that the grade can change by 0.003% for every 30 meters of track. In this case, the grade is changing from +0.08% to -0.07%. This is a change of 0.15%. The length of the transition curve is therefore 0.15% / 0.003%/30 m = 150 m.

Option B is incorrect because it is the length of the transition curve if the grade were changing from +0.08% to -0.07% at a rate of 0.002% per 30 meters.

Option C is incorrect because it is the length of the transition curve if the grade were changing from +0.08% to -0.07% at a rate of 0.004% per 30 meters.

Option D is incorrect because it is the length of the transition curve if the grade were changing from +0.08% to -0.07% at a rate of 0.005% per 30 meters.