Supporters of monorail and other sleek structures argue that because the structures are thinner than conventional rail viaducts, they’re cheaper and more aesthetic. They even argue that viaducts, which are more expensive than at-grade construction, are actually better. Transrapid does that, and Hyperloop does that as well. Hyperloop proponents specifically mention the the structure’s lighter weight as an explanation for the lower proposed cost – see my post update and the comments for extensive discussion and explanation for why the proposed Hyperloop costs are still an order of magnitude too low to be realistic.
Not having reliable construction costs for the intercity modes, I went and looked for construction costs of urban monorails, which are usually put above-ground, where their sleekness is a major advantage over conventional rail since they do not darken the street as much.
The resource with the most information is a JRTR article about Japanese intermediate-capacity rail, including both monorail and significantly less sleek automated guideway transit (AGT). It includes a diagram of monorail structures, which can be seen to be quite light and thin. The width of the structure from guideway to guideway is 4.5 meters including both guideway widths, and including the outside appears to raise it to 5.5. Two-track elevated conventional rail structures typically range from 7 to 10.5 meters wide.
The most recent Japanese monorail on the list, the Tama Monorail in suburban Tokyo, opened 1998, was $2.422 billion for 16 km: $151 million per km.
The one Japanese project more recent than the JRTR article, the Okinawa Monorail, built from 1996 to 2003, was $1.1 billion for 13 km: $85 million per km. The cost cited on the Monorail Society’s webpage is less than a third that amount. An extension to begin construction soon is projected at $350 million for 4 km, about the same cost per km.
Other Tokyo projects are not cheaper than the Tama Monorail. The AGT Yurikamome, opened 1995, cost $140 million per km as per JRTR; the Tohoku Jukan Line, a conventional elevated structure on top of an older elevated structure located in Central Tokyo, is $400 million for 1.3 km of new el and 2.5 additional km of new track on existing structure, which is $300 million per km if one considers the cost of everything except the new el to be zero, and about $150 million per km if the 2.5 km of existing structure is deemed to cost as much as at-grade rail, which is about half as much as an el typically. The ratio of elevated to underground cost is 2-3 and this is also in line with $150 million per km of baseline cost.
Outside Japan, we have the following projects, with their costs:
Chongqing Rail Transit Line 3: the first phase, built from 2007 to 2011, is ¥13.8 billion for 39 km, or in PPP dollars $88 million per km. About a third of the line is underground. An extension opened in 2013 cost ¥5.7 billion for 16.5 km (Chin.), or $85 million per km, all elevated. This is in a country where fully underground subways average about $150 million per km; but I cannot find cost figures for other lines in Chongqing itself, and any help would be appreciated.
Moscow Monorail: according to Wikipedia, 6.33 billion rubles in 2001-4, or $514 million in 2010 PPP dollars, for 4.7 km. This is $109 million per km, all elevated.
AirTrain Newark: the airport-internal people mover opened in 1996 and cost $354 million for 3 km, while the extension to the mainline train station was built from 1997 to 2000, added another 1.8 km to the project, and cost $415 million; both numbers are taken from the New York Times. Deflating both numbers to 1998, this is $1.03 billion for 4.8 km, or $215 million per km. In contrast, AirTrain JFK, a SkyTrain-like system, was $1.9 billion for 13 km and was built from 1998 to 2002, which in 2010 dollars is $185 million per km, actually lower than the cost of the monorail. Note that the AirTrain construction cost was not that high by normal-world standards: the same technology in Vancouver, in all-elevated configuration, is projected at C$116-150 million per km into Surrey when all elevated (see RRT alternatives 1 and 3 with distances of 15.5 km for 1 and 6 km for 3 as measured on a map), which is about US$95-120 million after PPP conversion. This is a 50-100% premium for New York over Vancouver prices, compared with a 400-600% premium for subway construction.
Palm Jumeirah Monorail, Dubai: Dh4.1 billion for 5.45 km, built 2006-8, about $1 billion in 2010 PPP dollars. This is $183 million per km, all elevated. Compare with the 17% underground Dubai Metro, mentioned in my previous post, which costs half as much per km.
Mumbai Monorail: the master plan is to spend 20,000 crore on 135 km, which after PPP conversion is $66 million per km. The under-construction first line is 3,000 crore for 19.54 km, or $69 million per km, all elevated. This compares with a parallel Mumbai Metro plan to build 146 km for 36,000 crore, or $111 million per km, of which according to Wikipedia 32 km, or 22%, is to be underground. This by itself suggests no monorail cost saving. But the first Mumbai Metro line is already over budget, at 3,800 crore, which again using Wikipedia for length (11.07 km) gives $154 million per km, all elevated. This suggests that in Mumbai there is a cost saving from using monorail, assuming all numbers are correct and that the Monorail Line 1 cost is not just the first phase, which is only 8 km.