The physical infrastructure is less of a constraint. The major problems are the road to the east of Phnom Penh to Neak Luong and the bridge over the Mekong River at that point.
The road is being upgraded by ADB and the bridge is already under construction with the assistance of the Government of Japan.
This is expected to result in more trade on the Phnom Penh to Saigon Port route, particularly as the port further develops and starts to handle more mainline vessels. The need for more permits confirms that demand on this route is high.
There is congestion through Phnom Penh and there have been proposals for a ring road, although trade moving along the corridor tends to be to from the city, rather than passing through.
There is unlikely to be significant road freight traffic from Thailand to Ho Chi Minh City, as most trade uses the maritime connection. Development of a bypass may be important domestically, but its significance on trade development is more difficult to assess.