how do i design an equall lane length track

hy, i,m going to route a track.[my ninco has so many lumps and bumps where the grandkids walk all over it]. the space is 16ft by 6ft 2 lane. i only have 2 criteria, it must have a long straight at the back with 2- 5ft6in outside radius bends on each end of the straight. the middle can be filled with anything as long as the lap lengths are roughly equall. could someone point me in the right direction. thanks. john