Trucks that utilise hybrid diesel-electric drive have been on the market for around 7 yrs at least. There are no really large size units yet, but they will probably appear sometime in the future.
The hybrid diesel truck concept is still effectively in the commercial-proving stage, but the ones in service are providing satisfactory service at lower daily operating cost and with reduced emissions, which are important in urban environments.
However, the diesel hybrid design is complex and comes with more electrical problems and "gremlins" than a regular diesel truck.
Then there is the higher maintenance levels as the hybrid ages. Batteries need to be replaced every few years, and there are more components overall, leading to higher maintenance costs. The diesel-hybrid resale value is also poor.
Then there is the higher potential for fires and electrical short circuits with hybrid designs, due to the substantial increase in the amount of wiring and electrical circuits and components.
The major setback for diesel hydrid market penetration is increased efficiency and cleaner emissions from the newer diesel engines. Regular diesel trucks are a well-proven concept with modest repair costs as compared to hybrids.
Thus, the diesel-hybrid truck (and bus) designs still have a way to go with efficiency gains and lowered "whole of life" owning and operating costs, before they can be proven to be a much more attractive option to purchasers.
Hino Hybrid Light Duty
Hino Trucks / Hino COE - Diesel and Diesel-Electric Hybrid
Volvo FE Hybrid - Volvo FE Hybrid : Volvo Trucks - United Kingdom & Ireland