how do you cross the river by highway 9, when motorcycles are not allowed on the highway?

There is no motorcycle ban on the western branch of Highway 9, just drive across with everyone else.

so, i will be ok if i enter motorway 9 at sukhumvit rd. and exit at ekkachi road.

thanks for your help. i am a new motorcycle rider in bangkok/thailand and do not want to have any issues.

Ah, highway 9 has two river crossings, it does look like the cable-stay bridge on the route you are talking about is restricted (the northern crossing isn't), best to actually explore.

Otherwise it's quite a detour

Sorry for any confusion.

one Troll / flaming post removed

You can use the Bhumibol bridges, normally bikes aren't allowed, but I have never seen police there.

If you really want it legal, you can use the ferry under the Bhumibol bridges for 10 baht.