Commuting trends: transit vs driving vs ...

[Pheidippides]

I think it is still too early for me to understand the question, but here is an attempt.

The costs (2016) are broken down this way:
Winter maintenance = $4,322 per lane km or $1.22 per m2 (assuming 3.65m lane width)
Total maintenance cost = $19,138 per lane km or $5.24 per m2 (assuming 3.65m lane width)
Total cost (including amortization, disposal, capital, maintenance) = $32,568 per lane km or $8.92 per m2 (assuming 3.65m lane width)

That would imply that the non-maintenance costs (capital, amortization, and disposal) are $13,430 ($32,568 - $19,138) per lane kilometer or $3.68 per m2.

A 1km stretch of 2 lanes of traffic (1 in each direction), each 3.65m wide, has an area of 7,300m2.
A 1km stretch of 2 lanes of traffic (1 in each direction), each 3.55m wide, has an area of 7,100m2.

A difference of 200m2 for every 10cm lane width reduction.

Not accounting for any inflation then...

Each year, the total cost of the original road is $65,136.
Each year, the total cost of the narrowed road is $63,351.
A difference of $1,785.

Each year, the total maintenance costs of the original road is $38,276.
Each year, the total maintenance costs of the narrowed road is $37,227.
A difference of $1,049.

Each year, the total winter maintenance costs of the original road is $8,644.
Each year, the total winter maintenance costs of the narrowed road is $8,407.
A difference of $237.

Each year, the total non-maintenance costs of the original road is $26,860.
Each year, the total non-maintenance costs of the narrowed road is $26,124.
A difference of $736.