Studies comparing motorway vs bike lane costs

https://activelivingresearch.org/sites/activelivingresearch.org/files/Dill_Bicycle_Facility_Cost_June2013.pdf

For example, the City of Portland calculated that the city’s entire bicycle network, consisting of over 300 miles of bikeways would cost $60 million to replace (2008 dollars), whereas the same investment would yield just one mile of a four-lane urban freeway.

...bicycle lanes can often be added to streets as part of planned maintenance or re-striping projects at a cost of $1 - $5 per foot (excluding right of way acquisition and engineering costs). Bicycle boulevards... generally cost between $9.50 and $27.20 per foot.

Assume values are US Dollars from 2008. Portland is fairly close to Canada, and the 300:1 ratio is mentioned, fortunately the units cancel out.

The only niggle I can see is that a 4 lane freeway has four lanes, whereas the bike lane's width is not stated. So it could be 75:1 ratio, or 1200:1 if the boulevard could take 16 bikes side by side.

https://www.seattletimes.com/seattle-news/politics/12-million-per-mile-for-a-bike-lane-that-should-trigger-a-civic-heart-attack/

Rather infamously, a bike lane in downtown Seattle recently cost $12 million for 1 mile! In any study, it's important to determine what was included in the costing. Freeways/motorways typically do not include intersections and signaling. Bike lanes typically do not include lighting but may have more or less involved side barriers and traffic light signalling systems included in their cost. Land acquisition costs are often the biggest cost component, but are not counted in calculations like that above for rebuilding Portland's lanes.

This answer explores the theoretical cost differences between building equivalent roads and bike lanes. It does not put any dollars on the costs as these include much more than the road / bike lane itself (rails, markings, signs, lights, noise protection, etc.) that depend heavily on the exact location.

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First, we need to ensure that the bike lane and the motorway are actually comparable. I'll take the throughput for this, the count of vehicles passing any point within a given time span:

• Assume that cars drive 100 km/h and keep a safety distance of 30m. With the length of a car (5m), we get a rate of 100000/35 = 2900 cars per hour.

• Assume that bikes drive 20 km/h and keep a safety distance of 6m. With the length of a bike (2m), we get a rate of 20000/8 = 2500 bikes per hour.

Ok, so a single lane of 100 km/h motorway has about the same throughput as a single lane of bike path. However, bikes are not as wide as cars, and that is one point where you can get significant cost reductions: A 100 km/h road needs to allocate at least 3.5m width per lane (2.5m truck plus safety distances), a cycle path may get away with 1.5m (0.5m bike plus safety distances). I.e. the road consumes about twice the space that the bike lane consumes.

Another factor is the robustness of the road. I cannot give numbers on this, but 2t cars to 40t trucks at 100 km/h put a lot more stress on the road than 100kg cyclists do. The asphalt of the motorway needs to be much thicker and well-constructed than the bike lane to last the same amount of years/vehicles. However, road construction vehicles are heavy as well, and the bike lane needs to survive its own construction. As such, there is a lower limit on the robustness of a bike lane that has nothing to do with the traffic it's intended for. Nevertheless, you need significantly less material to construct 1 m^2 of bike path than you need for the same area of motorway.

You will find that studies from different regions will yield different ratios. A Dutch study will have taken place in the country with the highest cycling penetration and most extensive cycling infrastructure in the world, whereas UK or US studies will have taken place in countries where cycling is primarily seen as leisure, and modes of transport other than motor vehicles are often not accommodated at all.

This can lead to differences such as whether or not to take parking into account, or the environmental impact. Bicycles require very little space to park or maneuver, and their operation results in zero emissions. Motor vehicles, on the other hand, often cannot turn without going round the block in urban areas, require 5+ times more space to park, and emit quite a few toxic substances. Additionally, motor vehicles require much more infrastructure to resolve conflicts and keep up (a sense of) safety, such as lights and physical barriers to reduce speed or separate road users.

When comparing studies, take these potential differences into account. Good luck.