(adapted from Busey, P. 1990. Vehicular turf. Proc. Florida State Hort Soc. 103:352-355.)

Part 3 of 3

Design Alternatives

Design for vehicular turf requires partial sacrifice of soil agronomic qualities, and percolation benefits, in order to achieve suitable engineering benefits in traction and resistance to shear. Knowledge of the type, frequency, and distribution of vehicular traffic is important in knowing how this can be accomplished. For buses and other very heavy vehicles, and daily automobile use, it is possible that no grass-only system would be suitable. For moderate weekend passenger car activity (e.g, more than two or three uses per week), asphalt or exposed, compacted rock are commonly used in the driveway alleys, but grassed sands are used for the parking ranges. This is the most common system used (e.g., Tampa Stadium and Joe Robbie Stadium).

Grass parking at a Church

Big Top Flea Market used permeable recycled concrete aggregate for the driveway alleys, to further increase total percolation. The aggregate was laid on a geotextile material to provide enhanced stability. For light weekend traffic (average of no more than one usage per week), grassed sands appear to suffice for parking areas and driveway alleys, but not headers, aprons, nor entryways. Worship Center Baptist Church, Plantation, Florida, used 100% vehicular turf. Compacted "lime rock", 15 cm deep, was overlaid with 5 cm sand. The area was planted to a mixture of seed, but only 'Argentine' bahiagrass persists. The bahiagrass has held up well, and is free of weeds. A potential variation of this concept is to construct high-use driveway alleys with a compacted, impervious base covered by a thin layer of a sand rooting medium. To provide runoff, the driveways would be slightly crowned, while pervious parking aisles would have a slight swale to capture runoff and fine soil particles. The impervious base would provide a shallow, perched water table which would make moisture management difficult, but achievable, with separate zoning.

Grass pavers

A variety of soil stabilizing materials have been tested, with varying success. The ultimate goal of such materials is to attain 100% permeable pavement, and 100% turfgrass canopy. While not reducing turf damage, polypropylene fibers (e.g., VHAF) are an effective backup for sports turf fields which will become severely worn (1). Such fibers can interfere with grass establishment. Grass-paver complexes can enhance ground cover and turfgrass quality for some weaker grasses, but reduce quality for the stronger grasses (10). Some energy-absorbing materials cause problems for pedestrians (14), and problems in warm-season turf establishment. For grass-paver systems to withstand heavy traffic, they must absorb and safely disperse energy. Materials might also be added to improve the cohesiveness of sand, while maintaining percolation. Candidates for testing include calcined clay (8) and/or gravel, incorporated with specially selected sand. Mechanical impedance to root growth would be unavoidable, but tolerated by some turfgrass species.

Transitions from pavement to turf are prone to erosion.

Other design variations are needed for 100% turf parking areas. Larger radii should be planned for curves. The transition between natural turf and asphalt must be reinforced and feathered to withstand simultaneous energy sources (deceleration, turning, and change in elevation), which could result in separation of the edges.

Conclusions

Despite everyday successes of vehicular turf, and theoretical background, research is still needed to bring this concept to standard design specification. However, some generalizations are supported from experience. Light (two to three uses per parking space per week) parking is supported by turfgrasses in Florida, especially bahiagrass, on sand soil, but areas more heavily trafficked often need reinforcement. Grasses such as zoysiagrass which tolerate high mechanical impedance perform well in, or on top of, gravel and rock. Adequate irrigation must be available for turf parking. Tree shade is very detrimental to traffic tolerance, and it should be remembered that bahiagrass and bermudagrass are the least shade tolerant turf species in Florida.

No planning, no success

Despite potential problems which occur from parking on the grass, the practice is widely successful. It is ironic that the immediate rationale for high impact turf is very often economic savings, not environmental. Vehicular turf distributes natural air conditioning to places where there are people, improves percolation to aquifers, and is enjoyed where it is used appropriately. If environmental benefits were more often considered first, designers might allocate the same resources for vehicular turf as for asphalt. Increased interest in alternatives could result in greater use of paver complexes, calcined clay, and other (as yet unperfected) materials, to make 100% turf a reality for public facilities throughout Florida. Because of their versatility, turf lots could provide overflow parking for shopping centers and other retail establishments. Compared with the asphalt alternative, many patrons would welcome the sight of a sea of grass.

Summary

Turfgrass in Florida is used for intermittent parking and driving of vehicles. In contrast to asphalt, turf provides environmental benefits: natural air conditioning, percolation, visual attraction, and flexibility for alternate use. This practice demonstrates the great utility of turfgrass, and violates the adage against walking on the grass. Dense, knitted turf roots bind sand, and improve traction resistance. Warm-season turfgrasses are comparatively wear tolerant, due to their reinforced vascular bundles. Unlike temperate areas, sand soils predominate in Florida, thus compaction problems can be minimal. Potential problems from traffic in turf in Florida are instability for heavy vehicles, need for appropriate grading and drainage design, and lack of motorist familiarity.

Literature Cited

1. Adams, W. A. and R. J. Gibbs. 1989. The use of polypropylene fibers (VHAF) for the stabilisation of natural turf on sports fields. p. 237-239 In: H. Takatoh (ed.). Proc. Sixth Int. Turfgrass Res. Conf., Tokyo, Japan. 31 July-5 August, 1989. Japanese Soc. Turfgrass Sci. and Int. Turfgrass Soc., Tokyo, Japan.
2. Beard, J. B. 1973. Turfgrass: Science and culture. Prentice-Hall, Englewood Cliffs, NJ.
3. Bingaman, D. E. and H. Kohnke. 1970. Evaluating sands for athletic turf. Agron. J. 62:464-467.
4. Brown, K. W. and R. L. Duble. 1975. Physical characteristics of soil mixtures for golf green construction. Agron. J. 67:647-652.
5. Carrow, R. N. and B. J. Johnson. 1989. Turfgrass wear as affected by golf car tire design and traffic patterns. J. Amer. Soc. Hort. Sci. 114:240-246.
6. Gibbs, R. J., W. A. Adams, and S. W. Baker. 1989. Factors affecting the surface stability of a sand rootzone. p. 189-191 In: H. Takatoh (ed.). Proc. Sixth Int. Turfgrass Res. Conf., Tokyo, Japan. 31 July-5 August, 1989. Japanese Soc. Turfgrass Sci. and Int. Turfgrass Soc., Tokyo, Japan.
7. Larcher, W. 1980. Physiological plant ecology. Springer-Verlag. Berlin.
8. Morgan, W. C., J. Letey, S. J. Richards, and N. Valoras. 1966. Physical soil amendments, soil compaction, irrigation, and wetting agents in turfgrass management: I. Effects of compactability, water infiltration rates, evapotranspiration, and number of irrigations. Agron. J. 58:525-535.
9. Shearman, R. C. and J. B. Beard. 1975. Turfgrass wear tolerance mechanisms. II. Effects of cell well constituents on turfgrass wear tolerance. Agron. J. 67:211-215.
10. Shearman, R. C., E. J. Kinbacher, and T. P. Riordan. 1980. Turfgrass-paver complex for intensively trafficked areas. Agron. J. 72:372-374.
11. Swartz, W. E. and L. T. Kardos. 1963. Effects of compaction on physical properties of sand-soil-peat mixtures at various moisture contents. Agron. J. 55: 7-10.
12. Taylor, S. E. and G. Pingel. 1971. Asphalt and artificial turf. Missouri Bot. Gard. Bull. 69:26-29.
13. Waldron, L. J. and S. Dakessian. 1982. Effect of grass, legume, and tree roots on soil shearing resistance. Soil Sci. Soc. Am. J. 46:894-899.
14. Wood, G. M. 1973. Use of energy-absorbing materials to permit turf growth in heavily trafficked areas. Agron. J. 65:1004-1005.
15. Youngner, V. B. 1961. Accelerated wear tests on turfgrasses. Agron. J. 53:217-218.

Vehicular turf, an alternative viewpoint.

Acknowledgments

Florida Agricultural Experiment Stations Journal Series No. N-00312. I thank Ms. Alyson Utter, R.L.A., Anderson-Lesniak Associates Ltd. Inc.; Mr. Marvin Gill, Big Top Flea Market; Mr. Charles M. Holder and Mr. Mike Jones, Central Florida Landscaping, Inc. of Tampa; Mr. Steve Shephard, Hillsborough County Parks Department; Mr. Jim Romeo, Joe Robbie Stadium; Mr. James E. Carter, Tampa Stadium; and Ms. Nina S. Carter and Rev. David Holt, Worship Center Baptist Church, for sharing their experience and insight. The need for this information was identified by Ms. Dani Lee, to whom I am grateful.

03 May 1998

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