• Stations, land. There are two ways to determine the number of stations:

1. As a function of mainline guideway mileage, the rule is one station every 1/2 mile. So the number of stations is easily determined with the calculation: 267.8 miles x 2=535.6
2. As a function of average number stations needed to serve a square mile. In the following illustration, the square is one square mile, and each circle (1/4 mi radius) and portion of a circle describes the service area of a station.

Adding up the circles & parts of circles results in a count of 4 stations. So, to serve 8.37²=70 square miles you need 4 x 70=280 stations. We will use this figure, as the goal of the PRT system is to cover square mileage.
     A least-cost strategy will be assumed for siting stations-- wherever possible co-locating them on the site of existing public uses such as fire stations, branch libraries and other public buildings, schools, and on the edges of parks. It is also expected that a number of stations would have part of their costs shared by private developers-- for example, a mall owner which would see an advantage to having PRT bringing shoppers right to the front door. Perhaps deals could be arranged, with the PRT company/agency paying for the station, with the land privately donated.

  • Vehicles. Skyloop costs included a vehicle of an initial cost of $25,911, 39 vehicles per system mile, for a total of 500. Thus, a 308 mile system results in a total of 39 x 308=12,012. This is clearly too many, and we will adjust it shortly.

  • Support. The Skyloop estimate includes realistic projections for such items as right of way, power, a number of bridge crossings, utility relocation, and design. Thus, for this exercise they do not need to be computed separately. Guideway is mounted on posts in public right of way, purchase of land on which to erect guideway will be the exception rather than the rule.

Station siding. Above we estimated 40.2 miles of siding. But then we calculated 280 stations-- resulting in 758 feet of siding per station. Intuitively this is a little too much. Instead, we'll assume 100 feet per acceleration and deceleration section, and 12 feet per station berth. (For comparison, consider that a typical city lot is about 40 ft. wide.) Also assuming a rough average of 3 berths per station, and the total is 236 feet of siding per station, or 12.52 miles for all 280 stations. Guideway by itself in Skyloop was $2.27 million/mile ($362/ft) for guideway and support posts. Thus, we can deduct 27.7 miles of siding and $62.9 million from the estimate. Total guideway mileage is now 308-27.7= 280.3.

Number of vehicles. Above we showed how the Skyloop vehicle fleet, when multiplied to the size of a 308 mile system, results in a 12,012-vehicle fleet. As an alternative, we will use a fleet size of 5,000 Taxi 2000 vehicles, which could have a capacity of over 39,000 trips per hour (as discussed in the essay on Capacity). So, the number of vehicles can be reduced by 7,012, at a cost saving of (7012 x 25911)= $181,687,932.

Station cost. Skyloop's 30 planned stations accounted for $11,156,012 of the total $109.44 million capital cost estimate. This breaks down as: $281,800 for each of 21 free-standing stations; $563,600 for each of 7 stations attached to existing buildings; $646,506 for each of two "storage barn" stations. For now we will ignore the storage stations. Applying these costs directly to the elttaeS context leads to a cost of [(280/28)x 9,863,000]= $98,630,000.
     In adjusting this cost, we will first look at the costs of one station, which assumes 3 berths:

     In the real world, not all stations would have 3 berths. We will adjust costs for an assortment of differently-berthed stations as:

     Next, we will allocate the elttaeS network's 280 stations as follows:

     Finally, our total station costs are:

Type	#	Unit	Total
1 berth stations	98	$210,800	$20,658,400
2 berth stations	28	223,800	6,266,400
3 berth stations	98	281,800	27,616,400
6 berth stations	28	369,600	10,348,800
12 berth stations	28	680,200	19,045,600
Total	280		$83,935,600

     Thus, we can deduct ($98,630,000-$83,935,600)= $14,694,400 from the preliminary estimate.

Network periphery. It is also not necessary for the edge of the network to be a straight line, the requirement only is that the guideway reach stations that have the edge within their service area. The most efficient way to do this is remove every other segment along the periphery. Thus, the northwest corner of the network would look like this:

Since each segment is .523 mi. (the guideway spacing) the amount of guideway removed is [(.523 x 7) x 4]= 14.6 miles, a deduction of ($2.27 mil/mi x 14.6)= $33.14 million. Total guideway mileage is now 280.3-14.6= 265.7 miles.

Guideway support posts. The Skyloop estimate included $4.67 million/mile for posts & foundations which hold up the guideway. This number was based on spacing the supports 60 feet apart (88 posts/mile, $4,135/post). However, subsequently Taxi 2000 Corp. determined that the supports could be spaced 90 feet apart and still do the job. So, the eltteaS network costs can be reduced by [88-(5280/90)]x 4,135= $121,293/mile, or (265.7 x 121,293)= $32.2 million over the whole system.

Central facility/storage. Skyloop planned a 7000 sq. ft., $843,000 facility to house its control center and central maintenance/repair operations. This cost is $65,654 for each of Skyloop's 12.84 miles, or $20.2 million if we use the same rate for the much larger elttaeS system. Instead, we will assume a elttaeS facility four times the size and cost: 28,000 sq. ft., $3.4 million. This means we can deduct another ($20.2 million - $3.4 million)= $16.8 million.

Vehicle storage. Skyloop had the ability to store 317 vehicles (63% of the fleet) during low demand periods, such as late nights and early mornings. It should be noted at this point that "storage" in PRT has a completely different meaning than in a bus, light rail or monorail system. In conventional transit, nearly entire fleets of huge vehicles must be regularly housed during times when few runs are scheduled. In PRT, because service is on-demand most vehicles are stored in the stations, waiting for passengers-- they are stored but in-service. Above we set the size of the fleet at 5,000 vehicles and the number of station berths at 952. What about vehicles in use? King County's average hourly transit demand (1998) is about 13,000, let's assume a demand in the middle of the night of 2,500 riders per hour. Also assuming a leisurely 3 trips per hour, 2,500 riders/hr could be served by 834 PRT vehicles.
     So far we've accounted for 952 vehicles stored in the system and 834 in use. Let's also assume a storage capacity of 500 at the central facility. That leaves a need to store 2,714. What do you really need to store 8-feet-long PRT vehicles for a few hours? All you really need is to park them on siding. Skyloop planned two $646,506 storage stations, merely siding with some type of awning to shelter the vehicles from the elements, with a capacity of about 120 vehicles each. Instead, let's assume short sections of storage siding scattered around the system, totaling (2714 x 8ft)=21,712 ft. We can now remove the Skyloop storage cost component from our estimate: $50,350/mile, $15.5 million for 308 miles, and replace it with (21,712 x 362)+[21712 x ((4135 x 59)/5280)]=$8.86 million worth of siding. This is a net reduction of $6.6 million