# Roadway Design

# Examples

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| **4R Examples**                                                       |
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| [Horizontal Curvature and Superelevation]{.underline}                 |
|                                                                       |
| The proposed alignment has 47 horizontal curves and the existing      |
| alignment has approximately 47 horizontal curves. All proposed        |
| horizontal curves will be designed using a maximum superelevation     |
| rate of 6% according to current AASHTO policy.                        |
|                                                                       |
| Due to the tight curvature of the existing road, some superelvation   |
| overlaps occurred and the superelevations were reduced in specific    |
| curves to remove overlap and to ensure super runoff and runout        |
| lengths were met. The superelevation runoff and runout lengths that   |
| were used were for a 6% superelevation rate. This was used so more    |
| curves could have some superelevation instead of the majority of the  |
| curves having no superelvation.                                       |
|                                                                       |
| [Vertical Curvature]{.underline}                                      |
|                                                                       |
| A best-fit design profile was established for the corridor to review  |
| the vertical curves and make recommendations for correcting the       |
| vertical profile. All proposed vertical curves meet the minimum       |
| AASHTO design standards. No design exceptions are anticipated.        |
|                                                                       |
| [Curve Widening]{.underline}                                          |
|                                                                       |
| The existing roadway corridor has little to no curve widening. The    |
| recommended curve widening is shown below in Table 2. The curve       |
| widening table shows the values that were determined during the first |
| five Generals Highway projects. They are considerably less than what  |
| is recommended by AASHTO. Based on the traffic characteristics of the |
| roadway, it is recommended that a 22-foot Motor Home be used as the   |
| design vehicle for the design of curve widening.                      |
|                                                                       |
| > **Table 2: Curve Widening**                                         |
|                                                                       |
| +---------------------------+-------------------------------------+   |
| | Curve Radius              | Curve Widening                      |   |
| |                           |                                     |   |
| | (feet)                    | (feet)                              |   |
| +---------------------------+-------------------------------------+   |
| | \>100                     | 0.0                                 |   |
| +---------------------------+-------------------------------------+   |
| | \<100                     | 1.0                                 |   |
| +---------------------------+-------------------------------------+   |
|                                                                       |
| Ten of the 47 curves require curve widening when using the 22-foot    |
| Motor Home design vehicle and table 2 criteria.                       |
|                                                                       |
| An additional 10 feet will be added to the roadway in the switchback  |
| areas. An additional 5 feet in both lanes will allow motor homes and  |
| trucks to make the sharp turn without encroaching into the other      |
| lane.                                                                 |
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| The route will generally follow the existing vertical and horizontal  |
| alignment with three exceptions. These exceptions, one at Bandit      |
| curve (approximately 90 m -- 150 m), the section near Glacier Creek   |
| (approx. 1300 m) and the switchback at Hollowell Park will be         |
| evaluated for potential realignment to improve safety, to ease the    |
| construction of the road and to decrease the impacts to Glacier       |
| Creek. The Moraine Park intersection will be re-aligned to create a   |
| standard 4-way intersection. The current configuration is offset. The |
| Mill Creek Ranger Station access road intersection, the Moraine Park  |
| "mail boxes" intersection, and the intersection at Beaver Meadows     |
| will also be realigned to create a standard T-intersection.           |
|                                                                       |
| The minimum radius curve for a 40 kph (25 mph) design speed is 43 m   |
| (141 ft). All of the proposed curves in the 40 kph section meet this  |
| criterion. The minimum radius curve for a 60 kph (35 mph) design      |
| speed is 123 m (403 ft). There are two curves within the 60 kph       |
| section which do not meet this criterion. The first substandard curve |
| is located at the beginning of the project, and the radius is 45 m    |
| (150 ft). The second substandard curve has a radius of 85 m (282 ft). |
| These design exceptions are required to minimize environmental and    |
| cost impacts. These design exceptions are listed on the Highway       |
| Design Standards form (See Appendix D). All vertical curves meet the  |
| stopping sight distance (crest) and headlight sight distance (sag)    |
| for 40 kph or 60 kph, as applicable.                                  |
|                                                                       |
| The selected design vehicle is the Thomas SLF230, with the following  |
| dimensions: Width of 2.44 m (8 ft), Track of 2.66 m (8.7 ft), Length  |
| of 9.4 m (30.8 ft), Front Overhang of 2.35 m (7.7 ft), Rear Overhang  |
| of 2.65 m (8.7 ft) and Wheelbase of 4.4 m (14.4 ft).                  |
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| Horizontal and vertical alignments generally follow the existing      |
| roadway, varying as described in typical section types above.         |
|                                                                       |
| > [Horizontal Alignment]{.underline}                                  |
| >                                                                     |
| > This portion of the project has nine exceptions to the minimum      |
| > radius. Increasing the radius in these areas would result in high   |
| > construction costs and unacceptable impacts to natural resources    |
| > due to the steep terrain, or violation of the rehabilitation        |
| > criteria.                                                           |
| >                                                                     |
| > Exceptions are generally at existing hairpin curves, and are        |
| > documented in the HDS form.                                         |
| >                                                                     |
| > [Superelevation]{.underline}                                        |
| >                                                                     |
| > Due to the low speed character of the roadway, a 6% maximum         |
| > superelevation rate was selected for the design. Exceptions to the  |
| > standard 6% criteria were determined to be warranted in the         |
| > following scenarios:                                                |
|                                                                       |
| -   Short curves with less than a 10 degree deflection -- matching    |
|     the existing alignment as much as possible resulted in numerous   |
|     short curves, often in successive reversing curve situations.     |
|                                                                       |
| -   Short curves with less than a 15 degree deflection, where the     |
|     downhill (potentially higher speed) direction has the benefit of  |
|     at least a 2% positive cross slope.                               |
|                                                                       |
| -   Selected Rehabilitation areas where adding superelevation would   |
|     result in slope impacts exceeding limits allowed by               |
|     rehabilitation criteria.                                          |
|                                                                       |
| > The HDS form documents the curves with exceptions to the minimum    |
| > superelevation criteria.                                            |
| >                                                                     |
| > [Vertical Alignment]{.underline}                                    |
| >                                                                     |
| > For Rural Collector Roads, AASHTO criteria allow a maximum of 11%   |
| > grade, and maximum grades of 14% to 16% for Rural Local Road        |
| > classifications. For Guanella Pass Road, a desirable maximum grade  |
| > of 9% was established during the EIS, due to operational, weather,  |
| > safety, and maintenance considerations. The HDS form documents      |
| > individual exceptions to the desired 9% criteria, along with the    |
| > justification for the exception.                                    |
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| **3R Examples**                                                       |
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| The horizontal and vertical alignments for the roadway generally will |
| not change. The horizontal alignment has been set to match as close   |
| as possible to the centerline of the existing road. There are four    |
| areas along the project where the horizontal alignment has been       |
| shifted.                                                              |
|                                                                       |
| The station ranges and reasons regarding horizontal alignment shifts  |
| are listed below:                                                     |
|                                                                       |
|   ------------------------------ -----------------------------------  |
|   Station Ranges                 Reason                               |
|                                                                       |
|   1+310 to 1+470                 Pull roadway away from cut slope.    |
|                                                                       |
|   1+740 to 2+050                 Center roadway on existing bench.    |
|                                                                       |
|   2+250 to 2+370                 Center roadway on existing bench.    |
|                                                                       |
|   2+800 to 3+300                 Pull roadway left away from cut      |
|                                  slope.                               |
|   ------------------------------ -----------------------------------  |
|                                                                       |
| The vertical profile along the project is intended to generally match |
| the existing, with the final grade being 0-50 mm above the existing   |
| grade. The profile may be varied to better balance the available      |
| quantity of millings.                                                 |
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| No modifications to the existing bench width are anticipated. The     |
| proposed roadway template will match the existing 24' paved traveled  |
| way and the existing 1' -- 2' shoulders. No changes to the existing   |
| curvilinear alignment and bench width are anticipated.                |
|                                                                       |
| There are three County Roads intersecting Wentworth Springs Road.     |
| They are Brauer Road, Breedlove Road, and Balderston Road. All        |
| remaining roads are private. There are approximately 40 private roads |
| and driveways. Construction easements may be required for work near   |
| the private roads and driveways. The speed is posted as 45 mph with   |
| several curves posted at 25, 30 and 35 mph.                           |
|                                                                       |
| At Balderston Road, there is a sight distance issue along the         |
| vertical curve just west of the intersection. One possible solution   |
| would be to lower the vertical curve, and regrade and clean the       |
| ditch. Determination if this improvement is within 3R scope will be   |
| necessary.                                                            |
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| The horizontal and vertical alignments for this roadway will not      |
| change. The extent of repair does not allow for revising the vertical |
| or horizontal alignment.                                              |
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