If you make the top portion and the right portion narrower, from 42" down to 30", you will be able to reach the tracks much easier. This will also give you more room 'inside' the layout, which you may find desirable. The wider portion on the left and bottom are accessible from both sides, so their width will not be a problem.
You could make the duck under, a fold down or lift up section, which will eliminate ducking under. There are many design options available to eliminate the duck under. you could use a bridge, or a drop down 'door' that could be fully landscaped. If you need more width, the drop down door is better.
The 2ft wide isles may be a problem, that is narrow and you may end up "running into" stuff on the edge of the train table. Better to have a minimum 3ft walkway. You have enough room to accommodate 3 ft walkways.
