Solution: (1) As shown in the figure, rays AD and AE intersect with L at points B and C, respectively, and BC is the section where the blind spot of viewpoint A is on the expressway.

(2) The intersection A is AF⊥BC, the vertical foot is point F, and the intersection DE is point H. 。

∵DE∨BC。

∴∠ADE=∠ABC,∠DAE=∠BAC.

∴△ADE∽△ABC，

∴AHAF=DEBC，

DE=30，AF=80，HA=40，

∴DEBC=AHAF，

∴30BC=4080，

∴BC=60m，

* The time for the car to drive at a constant speed through BC section of expressway is 3s.

The speed of the car is 60/3 = 20 (m/s).

The speed of the car is 20 meters per second.