University of Virginia Library

LECTURE 9 - ROUTE SURVEYS AND ALTERNATIVE LOCATIONS

Discussion:

Proposals for road construction start with a recognized need
for the extension of a road system for the purpose of economy of
transportation, social need, maintenance access, or scenic experience.
Feasibility studies are conducted by highway agencies based
on origin and destination counts to determine anticipated traffic
volumes. In the case of park roads, the feasibility of a road proposal
begins with the Master Plan.

Procedure:

The landscape architect starts the project with the study of
the route on USGS sheets and stereo pairs of aerial photographs.
In some cases, topo maps at larger scale are available. The U. S.
Forest Service and Soil Conservation Service use maps and aerial
photos at a scale of l″ = 660′ or 80 chains to a mile. Several
routes may be studied on paper using a 314 pencil to determine the
economy of construction in terms of excavation. In park road design
where preservation takes precedent over economy, a corridor is
selected to conserve natural and historical features within the
immediate area and on the viewshed as well.

Reconnaissance Survey:

Team members (engineer, geologist, biologist, resource manager,
landscape architect) walk the route using a compass or Brunton and
pacing distances. Flags are tied to tree limbs or on laths to mark
the line. The multidisciplinary team on the reconnaissance survey
argues over every detail along the route until agreement is reached.
The road then belongs to the Team! Once the flagged line is accepted,
the route is drawn on a topo base map.

Preliminary Survey:

Survey crews are then sent to map the flagged line from the
beginning to each flag measuring (chaining) horizontal distances
and recording deflection angles at each change in direction. It is
imperative that the survey be closed or tied-down to known survey
points at the ends of the line! The survey is drawn on paper and

given to the landscape architect for refinement—-curves and tangents
are drawn between P.I.s, the centerline is stationed, and the deflection
angles are plotted to establish deltas for each curve. The
landscape architect and engineer examine the line to confirm those
details of location made by the team in the field. Once the alignment
is approved and before more design time is invested in the
project, the proposal is presented at a public hearing with a rough
draft of an Environmental Impact Statement. In the case of state
or county roads, a right-of-way drawing is made showing the properties
affected by the alignment.

Location Survey:

The preliminary alignment is then drawn by the engineer and
staked in the field. Hundred-foot stations and the P.C.s, P.I.s
and P.T.s along the centerline are staked. Elevations are then
taken on all centerline stakes (hubs) and cross-sections are taken
by stadia. The engineer then refines the horizontal and vertical
alignment and produces the final plan-and-profile drawing. Earthwork
calculations and mass diagrams are made during design to insure
economy. Geometrics, grading plans, cross-sections, subsurface
drainage plans, pavement drawings, and profiles for ditches, are
prepared. In the case of grade separation structures, the structural
engineer and landscape architect work together to prepare detailed
drawings of the exterior features of the bridges and major structures.
After construction drawings are prepared a second public hearing is
held to review the final Environmental Impact Statement and the
final design.

Construction Surveys:

Centerline stakes, slope stakes, grade stakes, and off-set
stakes are then surveyed in to lay out construction. The first
operation by the contractor is clearing and grubbing the site which
often knocks out survey stakes and causes constant replacement by
a survey crew!

Supervision:

Project engineers are assigned to supervise construction and to
administer contracts on those projects designated Major Roads by

the National Park Service and the Federal Highway Administration
under the Interbureau Agreement of 1926. Minor Roads are those
designed by engineers and landscape architects in the National
Park Service working "in house" without help from Federal Highway.
In both cases, the landscape architect works hand in glove with the
engineer to merge their talents in the design and construction of
park roads.

Study of Alternatives:

The process of public review requires that alternative locations
be considered before the final location is approved. Once the
corridor is selected to preserve the natural and historic features
from the impact of construction, alternate routes may be considered
on the basis of economy.

A quick technique to study excavation cost is to draw a profile
of the groundline and then to superimpose a centerline profile.
Then draw quick cross-sections at representative locations to
determine the average conditions. Rough calculations can be made
to compare the earthwork required in each of the alternatives.

The Taking Line:

The R.O.W. line requires difficult judgments when private properties
are affected by the land necessary for acquisition. Land
acquisition teams are employed to establish reasonable offers to
land owners; fair market values are the rule. I encourage you to
argue for the owners in cases where their lands are separated by
the proposed R.O.W., or where their homes will be dangerously close
to the proposed roadway. You've seen homes situated at the toes
of slopes where the owners would have faired better if their entire
land had been acquired and they had been relocated. You've seen
farms divided by elevated roadways and pastures connected by long
culverts to let cattle move under road fills. We must do better!

GRADE SEPARATIONS AND INTERCHANGES

from Chapter X, A Policy on Geometric Design of Highways and Streets,
NCHRP, December 1979

"The greatest efficiency, safety, and capacity are attained when
intersecting through-traffic laws are separated in grades." "The
type of grade separation and interchange along with their design,
is influenced by many factors, the principle factor being design designation....traffic volume, character of composition of traffic,
design speed, and type of control of access."

Other controls: signing, economics, terrain, right-of-way.
Basic type of interchanges can vary extensively in shape and scope.

• Fig. X-1A-Trumpet or jug-handle ramp configuration

• Fig. X-1B-Three-level, directional, three-leg interchange

• Fig. X-1C-Not suitable for freeways but practical for highway-parkway
  connections where trucks are prohibited and
  design speed is low

• Fig. X-1D-Typical diamond which has variations with frontage
  road and collector-distributor ramps

• Fig. X-1E-Partial cloverleaf which favors heavier traffic volumes

• Fig. X-1F-Full cloverleaf generates weaving movements that must
  occur on collector-distributor roads

• Fig. X-1G-Fully directional interchange-example is four-stack
  interchange in Los Angeles

Open-road capacities can flow without interruption when intersecting
roads are separated by a structure. The high initial cost
of grade separations must be justified on the two considerations of
(1) elimination of traffic bottlenecks, and (2) correction of existing
hazards. Six items (or warrants) will justify an interchange:

1.

• Design Designation: whether or not the access will be fully
  controlled between terminals

2.

• Elimination of bottlenecks or spot congestion: inability to
  provide essential capacity of one or both roads

3.

• Elimination of hazard: locations of high accident frequency

4.

• Site Topography: physical properties of site make at-grade
  intersection impossible

5.

• Road-User Benefit: costs due to delays, fuel, time and
  accidents require improvement; relation of road-user benefit
  

  ---

  2

  
  
  
  to cost of improvement; annual benefit divided by annual
  cost of improvement; annual cost is sum of interest plus
  annual amortization.

6.

• Traffic Volume: volumes exceed capacity of at-grade intersection;
  elimination of conflicts greatly improves movement
  of traffic.

Additional Warrants:

1.

• Local streets cannot be terminated outside of right-of-way

2.

• Access to areas not served by frontage roads or other access

3.

• Railroad grade separations

4.

• Unusual concentrations of pedestrians such as parks on both
  sides of roadway

5.

• Bikeways or pedestrian crossings

6.

• Access to mass transit within major arterial

7.

• Free-flow aspects of certain ramps and completing geometry
  of interchange

ADAPTABILITY OF INTERSECTIONS

Three general types:

1.

• At-grade intersections - traffic on minor road may be delayed;
  up to 50% may be required to stop

2.

• Grade separations without ramps - through traffic is not
  delayed or interrupted

3.

• Interchanges - suited for heavy traffic volumes

SAFETY

Interchanges reduce conflicts of turning traffic and through
traffic, substituting instead the less hazardous merging and diverging
movements. All-right turn movements are safer than crossing and
stopping movements.

STAGE DEVELOPMENT

Allows partial completion to serve current conditions with option
to expand interchange to meet future traffic volumes.

ECONOMIC FACTORS

Initial cost is greater on interchanges; maintenance is also
greater; vehicular operating costs are generally lower at interchanges.

STRUCTURES

MAJOR STRUCTURES:

 

Bridges: -over streams, broad water -grade separations -elevated roadways -pedestrian crossings -bike crossings -railroads

Tunnels: -mountain ridges -ship channels -urban centers -airports

MINOR STRUCTURES:

 

Drainage: -culverts -diversions -impoundments

Other: -cribbing -retaining walls -cattle crossings

MISCELLANEOUS STRUCTURES:

       

Dams	Weigh stations	Emergency access
Breakwaters	Overhead signs	Lighting systems
Truck escape ramps	Cattle guards	Guardrails
Entrance gates	Maintenance access

DESIGN FACTORS:

a.

• Resistance to temperature changes, earthquake, bouyancy, earth
  pressure, erosion from chemicals or stream sediments, ice load

b.

• Live loads - weight and dynamics of vehicles including impact

  Dead loads - weight of structure itself

  Wind loads - may include flooding, ice, currents

c.

• Standard specifications for vertical and horizontal clearances

d.

• Special uses: heavy vehicles, railroads, saddle stock, construction
  equipment

BRIDGE TYPES:

         

Deck slab	spans up to 60 ft.	Note: Timber may be used for spans up to 20 feet.
Girder	spans up to 150 ft.
Truss	spans up to 300 ft.
Arch	spans up to 300+ ft.
Suspension	spans up to 1000+ ft.