The National Safety Council reports that 6 percent or more car crashes involved text messaging from a smartphone. In addition, many studies have found that cell phone while driving increases crash risk by 2.8 - 5 times (Klauer et al. 2006; Redelmeier and Tibshirani 1997; Violanti 1998; Violanti and Marshall 1996). With the inevitable prevalence of using portable devices during driving, it is probable that smartwatch usage behind the wheel may rise above smartphone usage. Unfortunately, previous literature seems to confirm the danger of smartwatch over smartphone usage while driving (Giang et al., 2014, 2015). However, these literatures unfairly assigned different notification settings (ringtone versus vibration) to each mobile device. This study compares simulator driving performance between smartphone and smartwatch at varying drive loads. Participants read text messages delivered either on a smartphone or smartwatch with notifications set to auditory only, vibration only or both (multimodal). Driving and texting performance was analyzed for each condition (phone vs. watch and auditory vs. tactile vs. multimodal and high vs. low drive load) to determine which device is more detrimental to driving performance. Interactions were observed between device and notification type for time to engage. Messages were answered faster on the watch with tactile and multimodal settings. Interactions between notification type and driving workload were detected for gain and coherence. More variability of gain was observed for the watch compared to the phone. In addition, tactile notifications had different levels of gain between drive load conditions compared to any other notification type. Both gain and coherence had higher levels in the high drive load compared to the load drive load conditions, indicating a possible underestimation of the driving environment.