There is a general notion among transportation professionals that having a longer additional lane length at a double-lane roundabout entry yields better performances. This paper investigates this notion using Lighthill-Whitham-Richards Model Analysis. Using Lighthill-Whitham-Richards model, a double-lane roundabout with additional lane design at the entry is analyzed. The additional lane lengths are varied at the entry in order to study the effect of different additional lane lengths on roundabout performance. A scalar hyperbolic partial differential equation (PDE) model for traffic velocity evolution based on the seminal Lighthill-Whitham-Richards (LWR) PDE for density is used. Equivalence of the solution of the velocity PDE and the solution of the LWR PDE is shown for quadratic flow rate functions. The results were then compared with similar lane length variations in VISSIM. The findings from this study are intended to provide transportation professionals with the ability to assess the effects of geometric design changes on operational performance. From the analysis presented in this paper, the delay and speed can be predicted from knowledge of the geometric parameters. While the design of an additional lane differs from a flared entry, findings from this study can also be applied to flare lengths if they are designed to operate in a similar fashion as additional lane entry used in this study.