On a per mile /per kilometre construction comparison, constructing highways is much cheaper, a highway being about half the cost of the rail track.
Per a 2014 report, the Valley Metrorail light rail transit system in the greater Phoenix, Arizona cost $1.4-bilion for a 20 mile double track or $35-milllion per mile for a single track whereas a typical highway costs about $20-million per lane mile. However the rail cost includes rolling stock, overhead electrical structure and railway yard for maintenance of the rolling stock.
It is because of this that Road lobby wins in many countries. It has done so in Pakistan at the expense of the neglect of the Railway network. However this is an incorrect comparison.
At 60-miles per hour carrying capacity of one lane highway is about 2,400 per hour or about 57,600 vehicles in a 24 hour period. About 75% of the cars carrying a single occupant most of the time, assuming the balance 25% carry 2 occupants, it means per lane capacity for 72,000 highway passengers.
What is missing here is cost of the motor vehicles. Before any passenger can benefit from the highway, he /she has to purchase a car or travel by the bus. Assuming average cost of $20,000 per vehicle, 57,600 vehicles would require additional investment of $1.15-billion. Thus actual cost for high way travel for a 20-mile single lane stretch is $400-million for the road plus $1.15-billion for vehicles or a total of $1.155-billion for 72,000 passengers, in other words $15,972 investment per passenger.
Assuming 80 passengers per train car, if each train consists of 5 cars and 6 trains per hour, capacity comes to 2400 passenger per hour or 57,600 passengers per mile per day at full capacity.
On this basis investment in a single rail network costing $700-milion is sufficient for 57,600 passengers or an investment of $9,896 per passenger.
The above being investment cost alone. Once we add fuel costs of the cars & the operating costs of the rail network, one would find that train travel comes out far cheaper than the travel by road. When you also consider the traffic congestion, pollution etc, rail travel wins hands down.
It is therefore a pity that instead of investing in upgrading railway network and in the light intercity & intra city trains Pakistanis has let the Pakistan Railways go to the dogs. Have heard that some people have even removed part of the track of the existing Karachi City Railway and sold the same as scrap!.
In my humble opinion, there is no need for Metro buses or high speed trains, 60-miles per hour trains are fine as long these run on time. If you want to improve the infra structure, rejuvenates Pakistan Railways & the Karachi Rail as the top priority before anything else.
Having been to Bombay (now Mumbai), please believe me when I say that without its rail network, Mumbai would cease to function. London come to stop whenever there is a Tube strike.
P.S.
I have only used single lane & single track for simplicity. Total investment for double track & two lanes would be twice as much. However, per passenger cost would not change as capacity would be doubled. I have used Phoenix Light rail dollar numbers because these available on the internet.