Help Please
 

Can any of my knowledgable friends here tell me.Why do US buses and Trucks (and maybe Japanese to) have 3 amber lights on the front roof of the cab? do they tell old bill how fast they are going ie: 1 light at 30mph ,2 at 40 etc. I have often wondered this ,or are they just for show, please explain . Regards, Alan

When we got Japanese trucks to test in the UK (in the 1970s) they were fitted with three green lights on the cab header rail (outside).
I believe that they did illuminate sequentially (or so I was told) so that the speed could be monitored. I've never seen it in writing (and we disconnected them).

I could be wrong but do believe they are called cab roof running lights and required by US law on vehicles over a certain weight or track width so when it is coming towards you instead of seeing just a pair of headlights you also see these running lights and think this is supposed to give a better indication of the vehicle size.

One night . . .
. . . the driver of a transporter loaded with cars had all his lights fail. The driver turned-on the headlights of the front car on the top deck so that he could see where to drive.
An approaching vehicle veered off the road into the verge. The transporter driver stopped and asked why the other driver had driven off the road and into the ditch. The motorist replied "I thought that if it was that high then how wide would it be . . . "

Nice one G-CPTN