Accessibility Futures

Paul Anderson, Pavithra Parthasarathi, and I recently completed a study looking at the accessibility impact of alternative land use and network scenarios for the Twin Cities. The full report is 767 pages! Most is Appendix, with maps of each scenario. The text is only 25 pages, including main figures. This post, drawn from the report, summarizes what we did and key findings.

Introduction

Transportation and land use are inter-dependent. The relationship between these two has been used to explain the growth patterns of cities, and continues to be influential in the decisions by businesses and individuals of where to locate in a city. Understanding this relationship is also important for planning future growth. Land use plans and transportation plans are typically conducted independent of each other, but the two need to be compatible if the goals of both are to be realized.

Accessibility is defined as the ability of people to reach the destinations to meet their needs and satisfy their wants, and has been long used in transportation planning. It is a function of both land use and the transportation network and can also be thought of as a measure of the efficiency of a city. This study develops a set of land use and transportation network scenarios, and evaluates accessibility for each scenario.

Transportation planning has traditionally focused on improving mobility and reliability measures of congestion across a metropolitan area. While policy based on these criteria can improve access to jobs or labor, there are other effects that result from this policy choice. First, mobility improvements, when this means improving the connectivity of outlying areas, tend to shape land use by encouraging decentralization. Second, focusing efforts only on reducing congestion is an automobile-centric policy that ignores and often reduces accessibility for people using other modes. Finally, congestion may not matter much as once thought. Accessibility increased across the Twin Cities metropolitan area from 1995 to 2005 even as traffic congestion worsened by most network measures.

Scenarios

This study analyzes the accessibility of 60 different scenarios, representing each combination of 6 land use scenarios and 10 networks. They are as follows.

Land Use

  • 2010 Land Use (LE)
  • 2030 Land Use (LF)
  • Centralized Population and Employment (LCC)
  • Centralized Population, Decentralized Employment (LCD)
  • Decentralized Population, Centralized Employment (LDC)
  • Decentralized Population and Employment (LDD)

Highway Networks

  • Freeflow (N0)
  • 2010 Highway Network (N1)
  • 2030 Highway Network (N2)
  • Diamond Lane Network (N4)
  • Congestion Pricing (N5)

Transit Networks

  • 2010 Transit Network (T0)
  • 2030 Transit Network (T1)
  • 21st Century Minneapolis Streetcars (T2) (includes T1)
  • 1932 Streetcars (T3) (includes T1)
  • Rhodium Network (T4) (includes T2)

TransitNets

Results

Looking across the different land use patterns, the highest person-weighed accessibility to jobs and to labor in almost all scenarios comes with centralized employment and population (LCC). The second highest is usually with centralized population and decentralized employment (LCD). However for labor accessibility, and the Met Council anticipated 2030 network (N2), decentralized population and centralized employment (LDC) slightly outperforms LCC and LCD. In all cases LCC has higher accessibility than fully decentralized growth (LDD).

In general centralizing population and decentralizing (LCD) employment produces more access to jobs than decentralizing population and centralizing employment (LDC), consistent with the suggestion of Levinson [9]. This scenario will also produce shorter commute times. It also usually produces more access to labor.

Compared to the forecast scenario, LCC produces about 20 to 25 percent more accessibility, depending on the network configuration.

Comparing networks, the freeflow network (N0) has the highest accessibility, followed by the Diamond Lane network (N4) (which has freeflow times on the freeway system inside the Beltway) (excluding the cost of tolls). The freeflow network (N0) has about 20 percent more accessibility than forecast network (N2). So if some technology could bring about freeflow travel, we would expect accessibility to be about 20 percent higher in peak. It is even greater for shorter time thresholds (i.e. the number of jobs that can be reached in 20 minutes increases more than 20 percent). The Diamond Lane network, which has freeflow times on freeways has about two-thirds as much gain as N0 compared to N2.

The anticipated 2030 network (N2) generally bests the existing 2010 network (N1) except when there is centralized population and centralized employment (LCC), but the two are very similar. Remember while the trip generation is the same across networks, the trip distribution is not, and depends on congestion levels. So adding to capacity in some areas will re-distribute demand and reroute traffic and thus shift congestion. While there may be a net reduction in congestion (this is
not guaranteed), the change in congestion will make some places more accessible and others less. The model nets this out and solves for the equilibrium. It turns out adding capacity in some places reduces accessibility to others. The added capacity in general adds about about 2 percent to 20 minute accessibility to jobs and 1 percent to 30 minute regional accessibility to jobs.

The congestion pricing scenario is similar to the Diamond Lane network, as person-weighed accessibility falls within +- 3 percent for all land uses. Congestion pricing is more effective than diamond lanes for 2010 and centralized land uses. This model accounts for the spatial benefits of tolling in terms of reallocating traffic to better routes, and some redistribution of traffic to different destinations, but does not fully account for time of day shifts, as the trip generation (by time of day) is fixed.

Transit accessibility is about twice as high in the centralized LCC vs decentralized LDD scenarios, indicating transit works significantly better at connecting people to jobs at higher densities.

Conclusions

At first glance, it would be easy to pick out the combination of land use and network with the highest accessibility and select that as the planning goal. Although the combination of centralized population and employment on a freeflow network might be ideal, it is likely not cost-effective or feasible under current technologies. Trying to achieve this combination would mean working against both the trends of increasing congestion (due to population growth) and decentralization of population and employment. Instead, the best use of these results are the comparisons that can be made.

First, a change in land use is more effective than the anticipated changes in the network, though moving to a freeflow network (through technological change or through pricing) would have significant time accessibility improvements (20 percent) though clearly at some monetary cost. Earlier studies came to the conclusion that network changes have a more local effect while land use changes have a regional effect. That is confirmed here, and one of the strongest arguments in favor of this conclusion is a comparison between the centralized population /decentralized employment and the decentralized population / centralized employment scenarios. The Twin Cities have highway and transit networks that were designed to serve a decentralized population commuting to centralized employment, and yet reversing this land use trend has higher accessibility, as it can make use of under-utilized capacity in the off-peak direction. This is not so surprising on the highway networks, as they work just as well for reverse commutes, but is interesting to see for the transit network as they are still designed to bring commuters into downtown.

Another observation is that there is much more differentiation between highway scenarios than between transit scenarios. On one hand, this reflects that the current highway network is congested during peak periods and some of the scenarios presented here (freeflow and congestion pricing, especially) dramatically increase speeds on the network. On the other hand, the clustering of transit results suggests that low transit accessibility is primarily caused by low transit speeds and not by a lack of transit coverage. The fact that the scenario that most expands service area, the 2030 base, has the lowest elasticity supports this claim.

The results of this study show that accessibility measures are a viable tool for comparing planning scenarios. With a selection of possible scenarios as broad as this one, it would be difficult to select one as the best choice to implement without knowing more about the cost and feasibility of each option. If the trend of decentralized development is too difficult to reverse, an investment in congestion pricing or HOT lanes might be best. On the other hand, decentralized development renders the transit system ineffective and reduces the effectiveness of the highway system in connecting people to jobs. A concentrated effort for higher densities and infill development in the central cities would benefit accessibility the most, and this study shows that increasing the centralization of population is more important than centralizing additional employment. A good use for this type of analysis would be to prioritize investments and land use strategies based on how “accessibility-effective” they are, or how much accessibility per unit dollar of investment they deliver. In determining final investment and planning strategies, the value of accessibility to jobs or labor needs to be traded off against other values.

NetworkBarwoMC


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7 Responses to Accessibility Futures

  1. Brendon Slotterback
    Brendon Slotterback June 1, 2012 at 4:16 am #

    How to measure cost? As part of the Met Council's regional framework update (now called "Thrive MSP 2040"), they assign/project population and jobs figures for each community. As I understand it, this is based on what they think may happen in each community based on existing plans, but also some amount of growth they feel the community should accommodate. The Met Council could make changes to this plan, like tightening restrictions on growth outside of the MUSA, protecting farmland and natural areas or (gasp!) increasing the minimum allowable planned density from 3.X units per acre to something more transit-, climate- and accessibility-supportive. These actions might have the effect of slowing decentralization and wouldn't necessarily "cost" anything upon adoption. A second or third order cost might be increased single family home or lot prices (if you don't include transportation costs). Second or third order savings might include reduced externalities, like ghg emissions from transportation and money spent on gas and autos. Some of these second and third order costs from land use regulation changes are more easily measurable than others, but generally tough to accurate estimate. Network change costs and savings are more easily measurable. My educated guess however, would be that if your goal would be to maximize accessibility, regional regulatory changes would be more cost-effective than network changes, but not necessarily more politically feasible.

  2. David Levinson
    David Levinson June 1, 2012 at 5:27 am #

    We were of course referring to network/infrastructure costs. The cost of rezoning is theoretically quite small (although we need to account for externalities and demands on public services somewhere). The cost of high-density vs. low-density housing, etc. would need to be accounted, but I don't think would be significant.

    Changing zoning may or may not increase actual densities. I am doubtful it has much effect. I.e. if you eliminated zoning in Minneapolis entirely, I would be surprised to see the population even 10% higher in 10 years (from 380K to 420K). The demand has to come from somewhere. Though lots of pundits seem to think zoning is the binding constraint, that is probably true in only a very few areas. I would be happy to eliminate zoning if we imposed appropriate impact fees etc.

    Clearly the politics are difficult, or it would be done by now.

    • Brendon Slotterback
      Brendon Slotterback June 1, 2012 at 8:56 am #

      I agree that zoning in the core is not as important. You can pretty much build as tall as you want downtown right now, but obviously there isn't overwhelming demand. The issue I was referring to is more about very little restriction on low density, non-contiguous development being allowed at the fringe. While the market for this development has decreased significantly recently, it will be back.

      • David Levinson
        David Levinson June 1, 2012 at 10:24 am #

        I think it will be very difficult to require minimum density zoning.

        We start with something undeveloped. It will be hard to say if you want to subdivide, you have to divide it into 160 parcels instead of say 2.

        On the other hand, it should be quite feasible to impose impact fees on the development that achieved similar ends due to high fixed costs, low variable costs. I am puzzled why Minnesota still does not allow these (apparently), when they are enabled in many other states. The MetCouncil could impose fees for Metropolitan services (sewer, water, transit, regional parks, regional roads), and the municipalities for local services (schools, roads, parks).

        In other words, if we price the externalities right, we get a lot closer to good form than trying to regulate it.

        Nevertheless, if we do this for the 7 county region, we will push development to the 13 ring counties, if we do this for the ring counties, we push development farther out to some extent, and so on. (compare growth in highly regulated Montgomery County Maryland vs. less regulated Fairfax County Virginia for an illustration). If people choose to live off the water and sewer grids, and don't get transit service, the metropolitan agencies won't have much claim for impact fees.

        • Brendon Slotterback
          Brendon Slotterback June 1, 2012 at 11:01 am #

          The Met Council already requires minimum density zoning in sewered areas of roughly 3 units per acre on average. Your local comprehensive plan won't be approved if you don't meet that (at least, that was the rule last time). They also say you shouldn't develop anything greater than 4 units per 40 acres outside the MUSA, but that hasn't been strictly enforced.

          I agree impact fees may be a better way to approach this issue, but as of now, not an option. Also folks living on septic without transit do impose costs – city, county and state roads. Also, they often times create long-term environmental liabilities that become very expensive to fix (failing septic tanks). Non-contiguous development on large lots also makes new dense growth more expensive when it does arrive because it's, well, non-contiguous. It also makes it much more politically contentious.

  3. David Levinson
    David Levinson June 2, 2012 at 4:01 am #

    Yet Met Council can't seem to actually require this though, i.e. some teeth are missing. I seem to see a lot of lots > than one-quarter or one-third acre around within the MUSA line. There are blocks (surface parking lots) with sewer service in downtown Minneapolis that don't have this or equivalent commercial density (though they are of course zoned for it). Even with zoning, you cannot mandate density.

    According to one source, Victoria, e.g. has minimum lot sizes of 15000 sq.ft. (there are 43560 ft^2 per acre, so this is less than 3 units per acre) (http://www.auditor.leg.state.mn.us/ped/pedrep/0103ch2.pdf … this may be old, I am not sure ), (looking at their actual code http://library.municode.com/index.aspx?clientId=1… it says in Residential District e.g. Buildings. "No building shall be located within 50 feet of a lot line.", which if my math is right and the average building is 40 ft x 40 ft requires a lot size of at least about 140×140 (19600 ft^2) .

    Victoria seems to be in the 2020 MUSA line: http://www.metrocouncil.org/about/facts/MUSAfacts

    I am not sure where the enforcement problem is (i.e. whether complying plans are adopted and ignored locally in zoning, or the plans themselves don't comply, or the averages compensate for the extremes somehow), but I would be happy if the Met Council actually did not provide water and sewer to low density properties. I.e. it would be much better for them to say, zone whatever you want, we just won't give you service if the density is too low, or we will charge you what it actually costs, rather than average cost.

    I think it is hard to establish minimum zoning, even if it is nominally official regional policy, because people in certain places (e.g. on the shores of Lake Minnetonka) might not want it. There are always loopholes, hobby farms, etc. to enable people with money to live on large lots away from the riffraff if they want to.

    Another loophole, big enough to drive a sewer through, zone according to law, subdivide according to law, develop every other lot. (No law, yet, makes you build contiguously AFAIK) Sell the intervening vacant lots to the adjacent landowners at time of first sale. To avoid the risk that some of them might eventually get built if the demand is there, put some sort of covenant/HOA regulation requiring adjacent lots in common ownership to be sold together. (IANAL, but it looks feasible).

    I think we agree about how the world "should" look (more or less). I think existing policies don't have a prayer of ensuring this, and the politics make it unlikely. No Metro area in the US has cracked this nut, ensures contiguous development, charges new development what it costs, and avoids negative externalities. The most regulatory (Portland, OR, Montgomery County, MD) promote leapfrog development across county and state borders. What is best if everyone does it may be worst if only one jurisdiction does it.

    Reducing zoning constraints or eliminating zoning (i.e. increasing densities) without compensating the losers (existing property owners who will receive negative externalities) somehow is in most places politically not viable.

    • Brendon Slotterback
      Brendon Slotterback June 3, 2012 at 8:56 am #

      The loophole you seek is the calculation by averages. It's also in the way they require calculation based only on newly guided/zoned land. Victoria can have larger lots if somewhere else in their plan they identify areas guided for higher density and the whole thing averages out to 3 units per acre (netting out some things like too, the list of which I can't remember). This calculation is also only done for areas the City is changing in their new plan, not an average across the entire city. This is how it was done during the last round of comp plan updates in 2008. At the very least, Met Council could tweak these rules to require the whole city average 3 units per acre, not just the new areas.

      A solution that may potentially be more effective, and is more along the lines of your recommendation for impact fees, I've discussed here. Simply require (at a regional level) that all new development more dense than 1 unit per 10 acres be sewered and require developers to cover all new infrastructure costs (at a city level). Obviously this requires backbone on the part of city's, which may be lacking, but it would expose large-lot sewered development to the full cost of the choice. I don't think it would really be considered an impact fee either.