How does the overall cost of the LLM-FHV network compare with the cost of a comparable conventional suburban road network? In this section, it will be shown that the overall infrastructure costs will probably be about the same, despite there being two networks in this plan. Several reasons contribute to this. First, LLM streets will be relatively inexpensive per meter of width per kilometer, because they do not have to be designed to carry heavy loads; they will not need traffic lights, sound walls, barriers or railings, medians, or any other roadside material except for street lights and signs; they will be narrow and thin enough so that water runoff can probably be handled by making the surface permeable rather than by constructing gutters and storm drains. Second, LLM roads will be much narrower than conventional suburban roads: an estimated average of 5.8 m, compared with an average of about 9.8 m in new suburbs (Delucchi 2005). Third, the FHV road network in the dual LLM-FHV
plan would also cost less per kilometer than a conventional FHV grid system, because it will carry less traffic, it will not need space for on-street parking, sidewalks, or bicycle lanes, and it will have fewer intersections and hence less of the cost associated with building and controlling intersections.
Finally, even though it might appear that the two complete road systems in the dual LLM-FHV plan would have roughly double the linear extent of a conventional FHV grid system, this is not the case since there are relatively few intersections in the LLM-FHV plan. As depicted in Figure 24.5a, the road has no cross streets and six housing lots line each side of the road. Figure 24.5b shows an intersection in which nine housing fronts line the roads (2 house fronts along each of the 4 arms of the cross, plus the one in the middle). Compared with a conventional grid system, the radial plan has relatively few intersections, and hence at a given housing, density will tend to have less road extent in the LLM or the FHV network.
In the single-family residential areas, there may be two or even three houses between each LLM and FHV (see Figure 24.3). No house borders the LLM and the FHV road, which means that no house has a road on both sides of it; each house does, however, share a driveway with one or two other houses. The alternative is for each house to have direct access to the LLM network on one side of it and to the FHV network on the other, via its own private drive, but it is suspected that most people will prefer to not have a road on both sides. The shared-driveway alternative illustrated in Figure 24.3 does entail longer driveways than in the road-on-both-sides alternative, but assuming that driveways are narrower than roadways, the net effect should be a reduction in paved area relative to the alternative in which there is only one house between each LLM and FHV road.
Considering all these factors, it is estimated that the total cost of the dual LLM-FHV street system will be equal to or even slightly less than the total cost of a comparable conventional suburban road network.
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