| Source | Model Type | R2 | Independent Variables |
| Andrady [7] | Logarithmic | Not Provided | RLo |
| Lee et al. [15] | Linear | 0.14 | Time |
| Migletz et al. [6] | Multiple Linear | Not Provided | Time, AADT |
| Aboud & Bowman [9] | Exponential | 0.58 | AADT |
| Fitch & Ahearn [8] | Logarithmic | 0.81 | AADT, Geographical Region |
| Sitzabee et al. [17] | Linear | 0.60 | RLo, Time, AADT |
| Rasdorf et al. [18] | Multiple Linear | Not Provided | Time |
| Karwa & Donnell [19] | Non-Linear | 0.26 | RLo, Time, AADT |
| Hollingsworth [20]
| Multiple Linear | Not Provided | RLo, AADT, bead type, color, lateral line placement, and time |
| Sarasua & Bell [1] | Linear | Not Provided | Time |
| Ozelim & Turochy [21] | Not Provided | 0.45 | RLo, Time, AADT |
| Malyuta [22] | Linear | 0.72 | Time, AADT |
| Wang et al. [23] | Linear | 0.57 to 0.68 | RLo, Time, ADT |